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Measuring instruments

Danfoss Measuring instruments Service guide

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Fitters notes Trouble shooting
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This chapter is divided into four sections:
Measuring instruments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
Fault location (Danfoss commercial refrigeration controls) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
Fault location in refrigeration circuits with hermetic compressors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185
Fault location overview (Danfoss Compressors) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197
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Contents Page
Instruments for fault location. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149
Classication of instruments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149
a. Uncertainty. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149
b. Resolution. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149
c. Reproducibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150
e. Temperature stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150
Electronic instruments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150
Check and adjustment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150
Adjustment and calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
Pressure gauges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
Service pressure gauges. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
Vacuum gauges. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
Thermometer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152
Hygrometer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152
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Notes
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Fitters notes Trouble shooting - Measuring instruments
CLASS N 1
90
Measuring Instruments
Instruments for fault location
Classication of instruments
The items of equipment most often used for locating faults in refrigeration systems are as follows:
1. Pressure gauge
2. Thermometer
3. Hygrometer
4. Leak detector
5. Vacuum gauge
6. Clamp ammeter
7. Megger
8. Pole nder
Ae0_0045
Instruments for fault location and servicing on refrigeration systems should full certain reliability requirements. Some of these requirements can be categorised thus: a. Uncertainty b. Resolution c. Reproducibility d. Long-term stability e. Temperature stability The most important of these are a, b, and e.
a. Uncertainty
b. Resolution
Ae0_0046
The uncertainty (accuracy) of an instrument is the accuracy with which it is able to give the value of the measured variable.
Uncertainty is often expressed in % (±) of either: Full scale (FS) or the measuring value. An example of uncertainty for a particular instrument is ±2% of measuring value, i.e. less uncertain (more accurate) than if the uncertainty is ±2% of FS.
Ae0_0047
The resolution of an instrument is the smallest unit of measurement that can be read from it.
For example, a digital thermometer that shows
0.1°C as the last digit in the reading has a resolution of 0.1°C.
Resolution is not an expression of accuracy. Even with a resolution of 0.1°C, an accuracy as poor as 2 K is not uncommon.
It is therefore very important to distinguish between the two.
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Fitters notes Trouble shooting - Measuring instruments
c. Reproducibility
e. Temperature stability
The reproducibility of an instrument is its ability to repeatedly show the same result for a constant measuring value.
Reproducibility is given in % (±).
d. Long-term stability
Long-term stability is an expression how much the absolute accuracy of the instrument changes in, say, one year.
Long-term stability is given in % per year.
Ae0_0003
The temperature stability of an instrument is how much its absolute accuracy changes for each °C temperature change the instrument is exposed to.
Temperature stability is given in % per °C. Knowledge of the temperature stability of the
instrument is of course important if it is taken into a cold room or deep freeze store.
Ae0_0004
Electronic instruments
Check and adjustment
Electronic instruments can be sensitive to humi­dity.
Some can be damaged by condensate if ope­rated immediately after they have been moved from cold to warmer surroundings.
They must not be operated until the whole instrument has been given time to assume the ambient temperature.
Never use electronic equipment immediately after it has been taken from a cold service vehicle into warmer surroundings.
Ae0_0005
Readings from ordinary instruments, and perhaps some of their characteristics, change with time.
Nearly all instruments should therefore be checked at regular intervals and adjusted if necessary.
Simple checks that can be made are described below, although they cannot replace the kind of inspection mentioned above.
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Fitters notes Trouble shooting - Measuring instruments
Check and adjustment (cont.)
Adjustment and calibration
Pressure gauges
The proper nal inspection and adjustment of instruments can be performed by approved test institutions.
Pressure gauges for fault location and servicing are as a rule of the Bourdon tube type. Pressure gauges in systems are also usually of this type.
In practice, pressure is nearly always measured as overpressure. The zero point for the pressure scale is equal to the normal barometer reading.
Therefore pressure gauges have a scale from –1 bar (–100 kPa) greater than 0 to + maximum reading. Pressure gauges with a scale in absolute pressure show about 1 bar in atmospheric pressure.
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Service pressure gauges
Vacuum gauges
As a rule, service pressure gauges have one or more temperature scales for the saturation temperature of common refrigerants.
Pressure gauges should have an accessible setting screw for zero point adjustment, i.e. a Bourdon tube becomes set if the instrument has been exposed to high pressure for some time.
Pressure gauges should be regularly checked against an accurate instrument. A daily check should be made to ensure that the pressure gauge shows 0 bar at atmospheric pressure.
Ae0_0009
Vacuum gauges are used in refrigeration to measure the pressure in the pipework during and after an evacuation process.
Vacuum gauges always show absolute pres-sure (zero point corresponding to absolute vacuum).
Vacuum gauges should not normally be exposed to marked overpressure and should therefore be installed together with a safety valve set for the maximum permissible pressure of the vacuum gauge.
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Fitters notes Trouble shooting - Measuring instruments
Thermometer
Hygrometer
Electronic thermometers with digital read-out are in widespread use for servicing. Examples of sensor versions are surface sensors, room sensors and insertion sensors.
Thermometer uncertainty should not be greater than 0.1 K and the resolution should be 0.1°C.
A pointer thermometer with vapour charged bulb and capillary tube is often recommended for setting thermostatic expansion valves. As a rule it is easier to follow temperature varia­tions with this type of thermometer.
Thermometers can be relatively easily checked at 0°C in that the bulb can be inserted 150 to 200 mm down into a thermos bottle containing a mixture of crushed ice (from distilled water) and distilled water. The crushed ice must ll the whole bottle.
If the bulb will withstand boiling water, it can be held in the surface of boilover water from a container with lid. These are two reasonable checks for 0°C and 100°C.
A proper check can be performed by a recog­nised test institute.
There are dierent types of hygrometers for measuring the humidity in cold rooms and air conditioned rooms or ducts:
Hair hygrometer Psychrometer Diverse electronic hygrometers
A hair hygrometer needs adjustment each time it is used if reasonable accuracy is to be maintained. A psychrometer (wet and dry thermometer) does not require adjustment if its thermometers are of high quality.
At low temperature and high humidity, the temperature dierential between wet and dry thermometers will be small.
Therefore, with psychrometers the uncertainty is high under such conditions and an adjusted hair hygrometer or one of the electronic hygrometers will be more suitable.
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Ae0_0013
Ae0_0014
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Hygrometer (continued)
A hair hygrometer can be adjusted by winding a clean, damp cloth around it and then placing it in an airtight container with water at the bottom (no water must be allowed to enter the hygrometer or come into contact with its bulb).
The container with hygrometer is then allowed to stand for at least two hours in the same temperature as that at which measurements are to be taken.
The hygrometer must now show 100%. If it does not, the setting screw can be adjusted.
Ae0_0049
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Fitters notes Trouble shooting - Fault location (Danfoss commercial refrigeration controls)
Contents Page
Fault location without . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
the use of instruments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
Categorisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
Knowledge of the system is required . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
Theoretical knowledge is necessary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158
Visible faults and the eect on the system operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
Air-cooled condenser . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
Water-cooled condenser . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
Receiver with sight glass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
Receiver stop valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
Liquid line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
Filter drier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
Sight glass. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
Thermostatic expansion valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160
Air cooler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160
Liquid cooler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160
Suction line. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161
Regulators in suction line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161
Compressor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161
Cold Room . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161
General. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161
Faults that can be felt, heard or smelled and the eect on the system operation . . . . . . . . . . . . . . . . . . . 162
Solenoid valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162
Filter drier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162
Faults that can be heard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162
Regulators in suction line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162
Compressor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162
Cold room . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162
Faults that can be smelled . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162
Cold room . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162
Refrigeration system with air cooler and air-cooled condenser . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163
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Notes
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Fitters notes Trouble shooting - Fault location (Danfoss commercial refrigeration controls)
Faults on refrigeration systems, general
Fault location without the use of instruments
This booklet deals with common faults in small, relatively simple refrigeration systems.
The faults, fault causes, remedies and eects on system operation mentioned also apply to more complicated and large systems.
However, other faults can occur in such systems. These and faults in electronic regulators are not dealt with here.
Ae0_0001
After gaining a little experience, many common faults in a refrigeration system can be localised visually, by hearing, by feel, and sometimes by smell. Other faults can only be detected by instruments.
Categorisation
Knowledge of the system is required
Ae0_0012
This booklet is divided into two sections. The rst section deals exclusively with faults that can be observed directly with the senses. Here, symptoms, possible causes and the eect on operation are given.
The second section deals with faults that can be observed directly with the senses, and those that can only be detected by instruments. Here, symptoms and possible causes are given, together with instructions on remedial action.
Ae0_0028
An important element in the fault location procedure is familiarity with how the system is built up, its function and control, both mechanical and electrical.
Unfamiliarity with the system ought to be remedied by carefully looking at piping layouts and other key diagrams and by getting to know the form of the system (piping, component placing, and any connected systems, e.g. cooling towers and brine systems).
Ae0_0029
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Fitters notes Trouble shooting - Fault location (Danfoss commercial refrigeration controls)
Theoretical knowledge is necessary
A certain amount of theoretical knowledge is required if faults and incorrect operation are to be discovered and corrected.
The location of all forms of faults on even relatively simple refrigeration systems is conditional on a thorough knowledge of such factors as:
The build-up of all components, their mode of operation and characteristics.
Necessary measuring equipment and measuring techniques.
All refrigeration processes in the system. The inuence of the surroundings on system
operation. The function and setting of controls and safety
equipment. Legislation on the safety of refrigeration
systems and their inspection.
Before examining faults in refrigeration systems, it could be advantageous to look briey at the most important instruments used in fault location.
Ae0_0033
In the following description of faults in refri­geration systems, sections 1 and 2 take as their starting points the piping diagrams, g. 1, 2 and
3. The systems are dealt with in the direction
followed by the circuit. Fault symptoms that can occur are described in circuit order. The description starts after the compressor discharge side and proceeds in the direction of the arrows.
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Ae0_0016
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Fitters notes Trouble shooting - Fault location (Danfoss commercial refrigeration controls)
Visible faults and the eect on the system operation Text in [ ] indicates fault cause
Visible faults Eect on system operation
Air-cooled condenser
a) Dirt, e.g. grease or dust, sawdust, dried leaves. Faults under a), b), c), d), e) create:
[Lack of maintenance]
b) Fan stopped.
[Motor defect] [Motor protector cut-out]
c) Fan rotates in wrong direction.
[Installation error] d) Fan blades damaged. e) Fins deformed
[Rough treatment]
Water-cooled condenser
with sight glass: See “Receiver”.
Receiver with sight glass
Liquid level too low.
[Insucient refrigerant in system] Vapour/vapour bubbles in liquid line.
[Overcharged evaporator] Low suction pressure or compressor cycling.
[Overcharged condenser during cold period] Low suction pressure or compressor cycling. Liquid level too high.
[Overcharged system] Excessive condensing pressure possible.
Receiver stop valve
a) Valve closed. System stopped via low-pressure control. b) Valve partly closed. Vapour bubbles in liquid line.
Liquid line
a) Too small Faults under a), b) and c) cause:
[Sizing error] b) Too long
[Sizing error] c) Sharp bends and/or deformed
[Installation error]
Filter drier
Dew or frost formation on surface. Vapour in liquid line.
[Filter partly blocked with dirt on inlet side]
Sight glass Risk of:
a) Yellow Acid formation, corrosion, motor burn-out, water freezing in
[Moisture in system] b) Brown Risk of wear in moving parts and blockage in valves and lters.
[Dirt particles in system] c) Pure vapour in sight glass. Standstill via low-pressure control or compressor cycling.
[Insucient liquid in system]
[Valve in liquid line closed] Standstill via low-pressure control.
[Complete blockage, e.g. of lter drier] Standstill via low-pressure control. d) Liquid and vapour bubbles in sight glass. All faults under d):
[Insucient liquid in system]
[Valve in liquid line partly closed]
[Partial blockage, e.g. of lter drier]
[No subcooling]
- Increased condensing pressure.
- Reduced refrigeration output.
- Increased energy consumption. For an air-cooled condenser, the dierence between air inlet and condensing temperatures should lie between 10 K and 20 K, preferably at the lower end.
For a water-cooled condenser, the dierence between condensing and water inlet temperatures should lie between 10 K and 20 K, preferably at the lower end.
Low suction pressure or compressor cycling.
Large pressure drop in liquid line. Vapour in liquid line.
thermostatic expansion valve.
Compressor cycling or running at low suction pressure.
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Fitters notes Trouble shooting - Fault location (Danfoss commercial refrigeration controls)
Visible faults and the eect on the system operation (cont.) Text in [ ] indicates fault cause
Visible faults Eect on system operation
Thermostatic expansion valve
a) Thermostatic expansion valve heavily frosted, frost on
evaporator only near valve.
[Dirt strainer partly blocked] [Bulb charge partly lost] [Previously described faults causing vapour bubbles in
liquid line]
b) Thermostatic expansion valve without external pressure
equalisation, evaporator with liquid distributor. [Sizing or installation error]
c) Thermostatic expansion valve with external pressure
equalisation, equalising tube not mounted.
[Installation error]
d) Bulb not rmly secured. Faults under d), e), f) lead to overcharged evaporator with risk of
[Installation error]
e) Entire bulb length not in contact with tube.
[Installation error]
f) Bulb placed in air current.
[Installation error]
Air cooler
a) Evaporator frosted only on inlet side, thermostatic expansion
valve heavily frosted.
[Thermal valve fault] [All previously described faults that cause vapour in
liquid line]
b) Front blocked with frost. Faults under a), b), c), d), e) cause:
[Lacking, incorrect or wrongly set up defrost procedure]
c) Fan does not run.
[Motor defect or motor protector cut-out] d) Fan blades defective. e) Fins deformed.
[Rough treatment]
Liquid cooler
a) Thermostatic expansion valve bulb not rmly secured. Causes overcharged evaporator with risk of liquid ow to
[Installation error] b) Thermostatic expansion valve without external pressure
equalising on liquid cooler with high pressure drop, e.g. coaxial evaporator.
[Sizing or installation error] c) Thermostatic expansion valve with external pressure
equalisation, equalising tube not mounted.
[Installation error]
Faults under a) cause operation at low suction pressure or compressor cycling via low-pressure control.
Faults under b), c) cause operation at low suction pressure or compressor cycling via low-pressure control. or compressor cycling via low-pressure control.
liquid ow to compressor and compressor damage.
Faults under a) cause: High superheat at evaporator outlet and operation at mostly low suction pressure.
- Operation with mostly low suction pressure.
- Reduced refrigeration output.
- Increased energy consumption. For thermostatic expansion valve controlled evaporators: The dierence between air inlet and evaporating temperatures should lie between 6 K and 15 K, preferably at the lower end.
For level-controlled evaporators: The dierence between air inlet and evaporating temperatures should lie between 2 K and 8 K, preferably at the lower end.
compressor and compressor damage. Faults b), c) cause:
- Operation with mostly low suction pressure.
- Reduced refrigeration output.
- Increased energy consumption.
For thermostatic expansion valve controlled evaporators: The dierence between air inlet and evaporating temperatures should lie between 6 K and 15 K, preferably at the lower end.
For level-controlled evaporators: The dierence between air inlet and evaporating temperatures should lie between 2 K and 8 K, preferably at the lower end.
160 DKRCC.PF.000.G1.02 / 520H1459 © Danfoss A/S (AC-DSL/MWA), 10 - 2006
Fitters notes Trouble shooting - Fault location (Danfoss commercial refrigeration controls)
Visible faults and the eect on the system operation (cont.) Text in [ ] indicates fault cause
Visible faults Eect on system operation
Suction line
a) Abnormally severe frosting. Risk of liquid ow to compressor and compressor damage.
[Thermal valve superheat too low]
b) Sharp bends and/or deformation. Low suction pressure or compressor cycling.
[Installation error]
Regulators in suction line
Dew/frost after regulator, no dew/frost ahead of regulator. Risk of liquid ow to compressor and compressor damage.
[Thermal valve superheat too low]
Compressor
a) Dew or frost on compressor inlet side. Liquid ow to compressor with risk of compressor damage.
[Superheat at evaporator outlet too low]
b) Oil level too low in crankcase.
[Insucient oil in system] System stop via oil dierential pressure control (if tted). [Oil collection in evaporator] Causes wear of moving parts.
c) Oil level too high in crankcase.
[Oil overlling] Liquid hammer in cylinders, risk of compressor damage: [Refrigerant mixed with oil in too cold a compressor] [Refrigerant mixed with oil because superheat too low
at evaporator outlet]
d) Oil boils in crankcase during start.
[Refrigerant mixed with oil in too cold a compressor] Liquid hammer, damage as under c)
e) Oil boils in crankcase during operation.
[Refrigerant mixed with oil because superheat too low at evaporator outlet]
Cold Room
a) Dry surface on meat, limp vegetables.
[Air humidity too low - evaporator probably too small] Leads to poor food quality and/or wastage. b) Door not tight, or defective. Can give rise to personal injury. c) Defective or missing alarm sign. Can give rise to personal injury. d) Defective or missing exit sign. Can give rise to personal injury. For b), c), d):
[Lack of maintenance or sizing error] e) No alarm system.
[Sizing error] Can give rise to personal injury.
General
a) Oil drops under joints and/or oil spots on oor.
[Possible leakage at joints] Oil and refrigerant leakage. b) Blown fuses.
[Overload on system or short-circuiting] System stopped. c) Motor protector cut-out.
[Overload on system or short circuiting] System stopped. d) Cut-out pressure controls or thermostats, etc.
[Setting error] System stopped.
[Equipment defect] System stopped.
- Damage to working valves.
- Damage to other moving parts.
- Mechanical overload.
Liquid hammer, damage as under c)
© Danfoss A/S (AC-DSL/MWA), 10 - 2006 DKRCC.PF.000.G1.02 / 520H1459 161
Trouble shooting
Fitters notes Trouble shooting - Fault location (Danfoss commercial refrigeration controls)
Faults that can be felt, heard or smelled and the eect on the system operation
Faults that can be felt Eect on system operation
Solenoid valve
Colder than the tubing ahead of the solenoid valve.
[Solenoid valve sticks, partly open] Vapour in liquid line.
Same temperature as tubing ahead of solenoid valve.
[Solenoid valve closed] System stopped via low-pressure control.
Filter drier
Filter colder than tubing ahead of lter.
[Filter partly blocked with dirt on inlet side] Vapour in liquid line.
Faults that can be heard Eect on system operation
Regulators in suction line
Whining sound from evaporating pressure regulator or another regulator.
[Regulator too large (sizing error)] Unstable operation.
Compressor
a) Knocking sound on starting.
[Oil boiling] Liquid hammer.
b) Knocking sound during operation. Risk of compressor damage.
[Oil boiling] Liquid hammer. [Wear on moving parts] Risk of compressor damage.
Cold room
Defective alarm system.
[Lack of maintenance] Can give rise to personal injury.
Faults that can be smelled Eect on system operation
Cold room
Bad smell in meat cold room.
[Air humidity too high because evaporator too large or load too low]
Leads to poor food quality and/or wastage.
Text in [ ] indicates fault cause
162 DKRCC.PF.000.G1.02 / 520H1459 © Danfoss A/S (AC-DSL/MWA), 10 - 2006
Fitters notes Trouble shooting - Fault location (Danfoss commercial refrigeration controls)
Refrigeration system with air cooler and air-cooled condenser
High discharge line temperature
Fig. 1
Low liquid level
High liquid level
High condensing pressure
Low condensing pressure
KP 15/17
High suction pressure
Low suction pressure
Hunting suction pressure
High suction
Compressor cycling
Hammer
High oil level
Low oil level
Oil boiling
Oil discoloured
Compressor cold
Compressor hot
Low temperature
DCL/DML
SGI/SGN
gas temperature
Low suction
gas temperature
EVR
Room temperature too low
Room temperature too high
Air humidity too high
Air humidity too low
KP 62
Frost blockage
Incomplete defrost
Frost only on thermal
valve and evaporator inlet
High superheat
Low superheat
Hunting
Periodic on/o
Constantly closed
Liquid
Vapour/liquid
SGI/SGN
Vapour
green
Colour yellow
brown/black
TE
© Danfoss A/S (AC-DSL/MWA), 10 - 2006 DKRCC.PF.000.G1.02 / 520H1459 163
Trouble shooting
Ae0_0019_02
Fitters notes Trouble shooting - Fault location (Danfoss commercial refrigeration controls)
Refrigeration system with two air coolers and air-cooled condenser
Fig. 2
Ae0_0030
164 DKRCC.PF.000.G1.02 / 520H1459 © Danfoss A/S (AC-DSL/MWA), 10 - 2006
Fitters notes Trouble shooting - Fault location (Danfoss commercial refrigeration controls)
KP 17
Refrigeration system with liquid cooler and water-cooled condenser
Fig. 3
Trouble shooting
Ae0_0035_02
© Danfoss A/S (AC-DSL/MWA), 10 - 2006 DKRCC.PF.000.G1.02 / 520H1459 165
Fitters notes Trouble shooting - Fault location (Danfoss commercial refrigeration controls)
Guide to fault location
Follow the arrows in the diagrams, gs. 1 and 3, p. 10/12. Begin after the compressor
Page
High condensing pressure ............................................................................................................................................... 167
Low condensing pressure ............................................................................................................................................... 167
Hunting condensing pressure ........................................................................................................................................ 167
High discharge line temperature...................................................................................................................................168
Low discharge line temperature ....................................................................................................................................168
Low liquid level in receiver .............................................................................................................................................168
High liquid level in receiver ............................................................................................................................................. 168
Refrigeration output too small ....................................................................................................................................... 168
Low temperature on lter drier ......................................................................................................................................168
Sight glass moisture indicator - discoloured, yellow ..............................................................................................168
Sight glass moisture indicator - brown or black.......................................................................................................168
Vapour bubbles in sight glass ahead of thermostatic expansion valve .......................................................... 169
Evaporator blocked by frost ........................................................................................................................................... 169
Evaporator frosted only on line near thermostatic expansion valve ................................................................169
Air humidity in cold room too high .............................................................................................................................. 170
Air humidity in cold room too low ................................................................................................................................ 170
Air temperature in room too high .................................................................................................................................170
Air temperature in room too low ...................................................................................................................................170
High suction pressure ........................................................................................................................................................ 170
Low suction pressure ......................................................................................................................................................... 171
Hunting suction pressure ................................................................................................................................................. 171
High suction gas temperature ........................................................................................................................................171
Low suction gas temperature ......................................................................................................................................... 171
Compressor cycling ............................................................................................................................................................ 171
Discharge tube temperature too high .........................................................................................................................172
Compressor too cold ..........................................................................................................................................................172
Compressor too hot............................................................................................................................................................172
Compressor knocking ........................................................................................................................................................172
Compressor oil level high .................................................................................................................................................172
Compressor oil level low ...................................................................................................................................................172
Compressor oil boils ...........................................................................................................................................................173
Compressor oil discoloured .............................................................................................................................................173
Compressor will not start .................................................................................................................................................173
Compressor runs constantly ..........................................................................................................................................174
166 DKRCC.PF.000.G1.02 / 520H1459 © Danfoss A/S (AC-DSL/MWA), 10 - 2006
Fitters notes Trouble shooting - Fault location (Danfoss commercial refrigeration controls)
System fault location
Symptom Possible cause Action
Condensing pressure too high
Air- and water- cooled condensers.
Condensing pressure too high
Air-cooled condensers.
Condensing pressure too high
Water-cooled condensers.
Condensing pressure too low
Air- and water-cooled condensers.
Condensing pressure too low
Air-cooled condensers.
Condensing pressure too low Water-cooled condensers.
Condensing pressure hunts
a) Air or other non-condensable gases in
refrigerant system.
Purge the condenser by using reclaim system, start and run system until it reaches running
temperature. Purge again if necessary. b) Condenser surface too small. Replace condenser with larger size. c) Refrigerant system charge too large (liquid
collection in condenser).
d) Condensing pressure regulation set for too high
Recover refrigerant until condensing pressure is
normal. The sight glass must remain full.
Set for the correct pressure.
a pressure. a) Dirt on condenser surface. Clean condenser. b) Fan motor or blade defective or too small. Replace motor or fan blade or both.
c) Air ow to condenser restricted. Remove air inlet obstruction or move condenser. d) Ambient temperature too high. Create fresh air inlet or move condenser. e) Incorrect air ow direction through condenser. Change rotation of fan motor. On condensing
units, air must ow through condenser and then to compressor.
f) Short-circuit between condenser fan airside
Install a suitable duct, possibly to outdoor air.
pressure and suction sides. a) Cooling water temperature too high. Ensure lower water temperature. b) Water quantity too small. Increase water quantity, possibly using
automatic water valve.
c) Deposits on inside of water pipes (scale etc). Clean out condenser water tubes, possibly by
deacidication.
d) Cooling water pump defective or stopped. Investigate cause, replace or repair cooling water
pump if tted.
a) Condenser surface too large. Establish condensing pressure regulation or
replace condenser. b) Low load on evaporator. Establish condensing pressure regulation. c) Suction pressure too low, e.g. insucient liquid
in evaporator.
Locate fault on line between condenser and
thermostatic expansion valve (see “Suction
pressure too low”). d) Compressor suction and discharge valves might
Replace compressor valve plate.
be leaking.
e) Condensing pressure regulator set for too low a
pressure.
f) Un-insulated receiver placed too cold in relation
to condenser (receiver acts as condenser).
Set condensing pressure regulator for correct
pressure.
Move receiver or t it with suitable insulating
cover. a) Temperature of cooled air too low. Establish condensing pressure regulation. b) Air quantity for condenser too large. Replace fan with smaller unit or establish motor
speed regulation. a) Water quantity too large. Install WVFX automatic water valve or set
existing valve. b) Water temperature too low. Reduce water quantity by using a WVFX
automatic water valve, for example. a) Dierential on start/stop pressure control for
condenser fan too large. Can cause vapour formation in liquid line for some time after start
Set dierential on lower value or use valve
regulation (KVD + KVR) or use fan motor speed
regulation.
of condenser fan because of refrigerant collection in condenser.
b) Thermostatic expansion valve hunting. Set thermostatic expansion valve for higher
superheat or replace orice with smaller size. c) Fault in KVR/KVD condensing pressure
Replace valves with smaller size.
regulating valves (orice too large). d) Consequence of hunting suction pressure. See “Suction pressure hunts”. e) Wrong sized or located check valve in condenser
line.
Check sizing. Mount check valve below condensor and close to receiver inlet.
Trouble shooting
© Danfoss A/S (AC-DSL/MWA), 10 - 2006 DKRCC.PF.000.G1.02 / 520H1459 167
Fitters notes Trouble shooting - Fault location (Danfoss commercial refrigeration controls)
System fault location (cont.)
Symptom Possible cause Action
Discharge line temperature too high
Discharge line temperature too low
Liquid level in receiver too low
Liquid level in receiver too high Refrigeration output
normal.
Liquid level in receiver too high
Refrigeration output too low (possible compressor cycling).
Filter drier cold, dew or frosting possible.
a) Suction pressure too low because of:
1) Insucient liquid in evaporator.
2) Low evaporator load.
3) Leaking suction or discharge valves.
4) Superheat too high in internal heat exchanger
or suction accumulator in suction line. b) Condensing pressure too high. See “Condensing pressure too high”. a) Liquid ow to compressor (thermal valve
superheat setting too low or bulb location
incorrect). b) Condensing pressure too low. See “Condensing pressure too low”. a) Insucient refrigerant in system. Investigate cause (leakage, overcharge in b) Evaporator overcharged.
1) Low load, leading to refrigerant collection in
evaporator.
2) Thermostatic expansion valve fault (e.g.
superheat setting too low, bulb location
wrong). c) Refrigerant collection in condenser because
condensing pressure is too low.
Refrigerant charge in system too large. Recover a suitable quantity of refrigerant, but
a) Partial blockage of a component in liquid line. Find the component and clean or replace it. b) Thermostatic expansion valve fault (e.g.
superheat too high, orice too small, lost charge,
partial blockage).
a) Partial blocking of dirt strainer in lter drier. Check whether there are impurities in the
Locate fault on line from receiver to suction line (see “Suction pressure too low”).
Ditto. Replace compressor valve plate. Omit heat exchange or possibly select smaller
heat exchanger.
See pages 175 and 176.
evaporator), repair fault and charge system if necessary.
See pages 175 and 176.
See pages 175 and 176.
Air-cooled condensers: Establish condensing pressure regulation by fan motor speed regulation, e.g. type RGE.
condensing pressure must remain normal and the sight glass free of vapour.
See pages 175 and 176.
system, clean out where necessary, replace lter drier.
b) Filter drier completely or partly saturated with
water or acid.
Moisture indicator discoloured Yellow.
Brown or black.
168 DKRCC.PF.000.G1.02 / 520H1459 © Danfoss A/S (AC-DSL/MWA), 10 - 2006
Moisture in system. Check system for leakage. Repair if necessary.
Impurities, i.e. small particles in system. Clean out system if necessary.
Check whether there is moisture or acid in the system, clean out where necessary and replace lter drier (burn-out lter) several times if necessary. If acid contamination is severe, replace refrigerant and oil charge, install DCR lter drier with interchangeable core in suction line.
Check system for acid. Replace lter drier, several times if necessary. In severe cases it can be necessary to change refrigerant and oil.
Replace SGI/SGN sight glass and lter drier.
Fitters notes Trouble shooting - Fault location (Danfoss commercial refrigeration controls)
System fault location (cont.)
Symptom Possible cause Action
Vapour bubbles in sight glass ahead of thermostatic expansion valve
Air coolers
Evaporator blocked by frost.
Air coolers Evaporator frosted only on line near thermostatic expansion valve, severe frost on thermostatic expansion valve.
Air coolers Evaporator damaged.
a) Insucient liquid subcooling from large
pressure drop in liquid line because:
1) Liquid line too long in relation to diameter.
Replace liquid line with tube of suitable diameter.
2) Liquid line diameter too small.
Replace liquid line with tube of suitable diameter.
3) Sharp bends, etc. in liquid line.
Replace sharp bends and components causing too large a pressure drop.
4) Partial blockage of lter drier.
Check for impurities, clean out if necessary, replace lter drier.
5) Solenoid valve defect.
b) Insucient liquid subcooling because of heat
penetration of liquid line, possibly from high temperature around liquid line.
See the chapter “Solenoid valves”. Reduce ambient temperature or install heat exchanger between liquid and suction lines or insulate liquid line, possibly together with suction line.
c) Water-cooled condensers: Insucient
subcooling because of wrong cooling water ow
Swap over cooling water inlet and outlet. (Water and refrigerant ow must be opposite).
direction. d) Condensing pressure too low. See “Condensing pressure too low”. e) Receiver stop valve too small or not fully open. Replace valve or open it fully. f) Hydrostatic pressure drop in liquid line too high
(height dierence between thermostatic
Install heat exchanger between liquid and suction lines ahead of rise in liquid line.
expansion valve and receiver too large). g) Badly or incorrectly set condensing pressure
Replace or reset KVR regulator at correct value. regulation causing liquid collection in condenser.
h) Condenser pressure regulation by start/stop of
condenser fan can cause vapour in liquid line for some time after fan start.
If necessary, replace regulation with condensing
pressure regulation via valves (KVD + KVR) or
with fan motor speed regulation, type VLT.
i) Insucient liquid in system. Recharge system, but rst make sure that none
of the faults named under a), b), c), d), e), f), g),
h) are present, otherwise there is a risk of the
system becoming overcharged.
a) Lack of or poor defrost procedure. Install defrost system or adjust defrost
procedure.
b) Air humidity in cold room too high because of
moisture load from:
1) Unpackaged items.
Recommend packaging of items or adjust
defrost procedure.
2) Air ingress into room through ssures or open door.
Repair ssures. Recommend that door be
kept closed.
Refrigerant supply to evaporator too small because of:
a) Thermostatic expansion valve defect, e.g.
See pages 175 and 176.
1) Orice too small.
2) Superheat too high.
3) Partial loss of bulb charge.
4) Dirt strainer partly blocked.
5) Orice partly blocked by ice.
b) Fault as described under “Vapour bubbles in
See “Vapour bubbles in sight glass”. sight glass”.
Fins deformed. Straighten ns using a n comb.
Trouble shooting
© Danfoss A/S (AC-DSL/MWA), 10 - 2006 DKRCC.PF.000.G1.02 / 520H1459 169
Fitters notes Trouble shooting - Fault location (Danfoss commercial refrigeration controls)
System fault location (cont.)
Symptom Possible cause Action
Air humidity in cold room too high, room temperature normal
Air humidity in room too low
Air temperature in cold room too high
Air temperature in cold room too low
Suction pressure too high a) Compressor too small. Replace compressor with larger size.
Suction pressure too high and suction gas temperature too low
Suction pressure too low, constant running
a) Evaporator surface too large. Causes operation at
excessive evaporating temperature during short running periods.
Load on room too low, e.g. during winter (insucient dehumidication because of short
total running time per 24 hours). a) Cold room poorly insulated. Recommend improved insulation. b) High internal energy consumption, e.g. lights
and fans. c) Evaporator surface too small, causes long
running times at mainly low evaporating
temperatures. a) Room thermostat defect. See the chapter “Thermostats:”. b) Compressor capacity too small. See “Compressor”. c) Load on room too high because of:
1) Loading of non-cooled items.
2) High energy consumption,
e.g. for lights and fans.
3) Cold room poorly insulated.
4) High air ingress.
d) Evaporator too small. Replace evaporator with larger size. e) Insucient or no refrigerant supply to
evaporator. f) Evaporating pressure regulator set for too high
an evaporating pressure. g) Cut-out pressure on low-pressure control set too
high. h) Capacity regulating valve opens at too high an
evaporating pressure. i) Opening pressure of crankcase pressure
regulator set too low. a) Room thermostat defect:
1) Cut-out temperature set too low.
2) Bulb location wrong.
b) Ambient temperature very low. If absolutely necessary, establish thermostat
b) One or more compressor disc valves leaking. Replace valve plate. c) Capacity regulation defective or incorrectly set. Replace, repair or adjust capacity regulation. d) System load too high. Recommend less load or replace compressor
e) Hot gas defrost valve leaking. Replace valve. a) Thermostatic expansion valve superheat setting
too low or bulb located incorrectly. b) Thermostatic expansion valve orice too large. Replace orice with smaller size. c) Leaking liquid line in heat exchanger between
liquid and suction lines. Low-pressure control set incorrectly, or defective. Adjust or replace low-pressure control KP 1 or
Replace evaporator with smaller size.
Establish humidity regulation with hygrometer, heating elements and KP62 safety thermostat.
Recommend less internal energy consumption.
Replace evaporator with larger size.
Recommend placing of smaller load or increased system capacity.
Recommend reduction of energy consumption or increased system consumption.
Recommend better insulation. Recommend repair of ssures and least possible
door opening.
See “Vapour bubbles in sight glass ahead of thermal valve” and pages 175 and 176.
Set evaporating pressure regulator at correct value. Use a pressure gauge.
Set low-pressure control at correct cut-out pressure. Use a pressure gauge.
Set capacity regulating valve at lower opening pressure.
Set valve for higher opening pressure if the compressor will withstand it.
See page 180.
controlled electrical heating.
with larger size, or install KVL crankcase pressure regulator.
See pages 175 and 176.
Replace HE heat exchanger.
combined pressure control KP 15.
170 DKRCC.PF.000.G1.02 / 520H1459 © Danfoss A/S (AC-DSL/MWA), 10 - 2006
Fitters notes Trouble shooting - Fault location (Danfoss commercial refrigeration controls)
System fault location (cont.)
Symptom Possible cause Action
Suction pressure too low, normal operation or compressor cycling
Suction pressure hunts Thermostatic expansion
valve operation.
Suction pressure hunts Electronic expansion
valve operation.
Suction gas temperature too high
Suction gas temperature too low
Compressor
Compressor cycling (cut-out via low-pressure control).
a) Low system load. Establish capacity regulation or increase
lowpressure control dierential.
b) Insucient refrigerant in evaporator, because of:
1) Insucient refrigerant in receiver. See “Liquid level in receiver too low”.
2) Liquid line too long. See “Vapour bubbles in sight glass.”
3) Liquid line too small. Ditto.
4) Sharp bends, etc. in liquid line. Ditto.
5) Filter drier partly blocked. See “Vapour bubbles in sight glass”.
6) Solenoid valve sticks. Ditto.
7) Inadequate liquid subcooling. Ditto.
8) Fault at thermal valve. See pages 175 and 176. c) Evaporator too small. Replace with larger evaporator. d) Evaporator fan defective. Replace or repair fan. e) Pressure drop in evaporator and/or suction line
too large.
If necessary, replace evaporator and/or suction line.
f) Lack of or inadequate defrosting of air cooler. Establish a defrost system or adjust defrost
procedure.
g) Freezing in brine cooler. Increase brine concentration and check frost
protection equipment.
h) Insucient air or brine through cooler. Check cause and correct fault. See “Air coolers”
and “Liquid coolers”. i) Oil collection in evaporator. See “Oil level in crankcase ton low” a) Thermostatic expansion valve superheat too
See pages 175 and 176.
low. b) Thermostatic expansion valve orice too large. c) Capacity regulation fault
1) Capacity regulating valve too large.
Replace KVC capacity regulating valve with smaller size.
2) Pressure control(s) for stage regulation
incorrectly set.
Set for greater dierence between cut-in and cut-out pressures.
Hunting normal None
Refrigerant supply to evaporator too small because: a) System refrigerant charge too small. Charge refrigerant to correct level. b) Defect in liquid line or components in that line See these entries: “Liquid level in receiver”, “Filter
drier cold”, “Vapour bubbles in sight glass”, “Suction pressure too low”.
c) Thermostatic expansion valve super- heat
See pages 175 and 176.
setting too high, or bulb charge partly lost. Refrigerant supply to evaporator too large because: a) Thermostatic expansion valve superheat set too
See pages 175 and 176.
low. b) Thermostatic expansion valve bulb located
See pages 175 and 176. incorrectly (too warm or in poor contact with piping).
a) Compressor capacity too high in relation to load
at any given time.
Establish capacity regulation using KVC
capacity regulating valve or parallel-coupled
compressors.
b) Compressor too large. Replace compressors with smaller size. c) Opening pressure of evaporating pressure
regulator set too high.
Using a pressure gauge, set KVP regulator at
correct value.
Trouble shooting
© Danfoss A/S (AC-DSL/MWA), 10 - 2006 DKRCC.PF.000.G1.02 / 520H1459 171
Fitters notes Trouble shooting - Fault location (Danfoss commercial refrigeration controls)
System fault location (cont.)
Symptom Possible cause Action
Compressor
Compressor cycling (cut-out via high- pressure control).
Discharge pipe temperature too high
Compressor
Compressor too cold.
Compressor Compressor too hot.
Knocking sound: a) Constant.
b) During start.
Compressor Oil level in crankcase too high. On high load, otherwise not.
During standstill or start
Compressor Oil level in crankcase too low.
a) Condensing pressure too high. See “Condensing pressure too high”. b) High-pressure control defect. Replace high-pressure control KP 5 / 7 or
combined pressure control KP 15 / 17.
c) High-pressure control cut-out set too low. Using a pressure gauge, set pressure control at
correct value. Avoid compressor cycling by using high-pressure control with manual reset.
Discharge pipe temperature too high. Replace valve plate. See also “Discharge
temperature too high”.
Flow of liquid refrigerant from evaporator to suction line and possibly to compressor because of incorrectly set thermostatic expansion valve.
a) Compressor and possibly motor overloaded
because evaporator load and thereby suction pressure too high.
b) Poor motor and cylinder cooling because of: Locate fault on line between condenser and
1) Insucient liquid in evaporator.
2) Low evaporator load.
3) Suction and discharge valves not tight.
4) Superheat too severe in heat exchanger,
or in suction accumulator in suction line. c) Condensing pressure too high. See “Condensing pressure too high”. a) Liquid hammer in cylinder because of liquid ow
to compressor. b) Oil boiling because of liquid build up in
crankcase. c) Wear on moving compressor parts, especially
bearings.
Oil quantity too large. Drain oil to correct level, but rst ensure that
Refrigerant absorption in crankcase oil because of too low an ambient temperature.
a) Oil quantity too small. Fill oil to correct level, but rst be sure that the b) Poor oil return from evaporator because:
1) Diameter of vertical suction lines too large.
2) No oil separator.
3) Insucient fall on horizontal suction line.
c) Wear on piston/piston rings and cylinder. Replace worn components. d) On compressors in parallel: In all circumstances: the compressor started last
1) With oil equalising tube:
Compressors not on same horizontal plane.
Equalising pipe too small.
2) With oil level regulation:
Float valve partly or wholly blocked.
Float valve sticking. e) Oil return from oil separator partly or wholly
blocked, or oat valve sticking.
Set thermostatic expansion valve for lower superheat using MSS method, see the chapter (Thermostatic expantion valves” or pages 175 and 176.”.
Reduce evaporator load or replace compressor with larger size.
thermostatic expansion valve (see “Suction pressure too low”).
Ditto Replace valve plate. Omit heat exchange or possibly select smaller
HE heat exchanger.
Set thermostatic expansion valve for lower superheat using MSS method.
Install heating element in or under compressor crankcase.
Repair or replace compressor.
the large quantity is not due to refrigerant absorption in the oil.
Install heating element in or under compressor crankcase.
oil quantity in the crankcase is not a result of oil collection in the evaporator. Install oil lock at 1.2 m to 1.5 m from vertical suction lines. If liquid supply is at the bottom of the evaporator it can be necessary to swap inlet and outlet tubes (liquid supply uppermost)
is most subject to oil starvation. Line up compressors so that they are in same
horizontal plane. Install larger equalising pipe. Fit vapour equalising pipe if necessary.
Clean or replace level container with oat valve.
Ditto. Clean or replace oil return pipe or replace oat
valve or whole oil separator.
172 DKRCC.PF.000.G1.02 / 520H1459 © Danfoss A/S (AC-DSL/MWA), 10 - 2006
Fitters notes Trouble shooting - Fault location (Danfoss commercial refrigeration controls)
System fault location (cont.)
Symptom Possible cause Action
Compressor
Oil boils during start.
Compressor Oil boiling during operation.
Compressor Oil discoloured.
Compressor Will not start.
a) High refrigerant absorption in crankcase oil
because of low ambient temperature.
b) Systems with oil separator:
Too much absorption of refrigerant in oil in separator during standstill.
Install heating element in or under compressor crankcase.
Oil separator too cold during start. Install thermostat-controlled heating element or solenoid valve with time delay in oil return tube. Fit non return valve in discharge pipe after oil separator.
a) Flow of liquid refrigerant from evaporator to
compressor crankcase.
b) Systems with oil separator: Float valve not
Set thermostatic expansion valve for higher superheat using MSS method.
Replace oat valve or whole oil separator.
closing completely. System contamination arising from: In all circumstances: Change oil and lter drier. a) Cleanliness not observed during installation. Clean out refrigerant system if necessary. b) Oil breakdown because of moisture in system. Clean out refrigerant system if necessary. c) Oil breakdown because of high discharge pipe
temperature.
Locate and remedy cause of excessive discharge pipe temperature. See “Discharge pipe temperature too high”. Clean out system if necessary.
d) Wear particles from moving parts. Clean out refrigerant system if necessary.
Replace worn parts or install new compressor.
e) Inadequate cleaning after motor burn-out. Clean out refrigerant system. Fit DA “burn-out”
lter. Replace lter several times if necessary. a) Insucient or no voltage for fuse group. Telephone electricity company. b) Blown group fuses. Locate fault. Have fault repaired and change
fuses. c) Fuse in control circuit blown. Locate fault. Have fault repaired and change
fuses. d) Main switch not on. Switch on. e) Thermal protection in motor starter cut out or
Locate and repair fault or replace protector.
defective, e.g. as a result of:
1) Excessive suction pressure.
2) Condensing pressure too high.
3) Dirt or copper deposition in compressor bearings, etc.
4) Supply voltage too low.
5) Single phase drop out.
6) Short-circuited motor windings (motor burn-out).
f) Motor winding protectors cut out because of
excessive current consumption.
See “Suction pressure too high”.
See “Condensing pressure too high”.
Clean out refrigerant system, replace compressor
and lter drier.
Telephone electricity company.
Locate and remedy fault (often blown fuse).
Clean out refrigerant system if necessary, replace
compressor and lter drier.
Locate and remedy cause of excessive current
consumption, start system when windings have
cooled down (can take a long time). g) Contactors in motor starter burnt out because:
1) Starting current too high.
Locate and remedy cause of motor overload,
replace contactor.
2) Contactor undersized.
h) Other safety equipment cut out, incorrectly set
or defective:
Replace contactor with larger size.
In all circumstances, locate and repair fault
before starting system:
Oil dierential control. (no oil, oil boiling). See “Compressor, Oil level too low” and
“Compressor, Oil boiling....”
High-pressure control. See “Condensing pressure too high”. Low-pressure control. See “Suction pressure too low”. Flow switch. (insucient brine concentration, brine pump failure, blocked brine circuit lter,
Locate and remedy cause of reduced or no ow
in brine circuit. See “Liquid coolers”.
evaporating temperature too low). Frost protection thermostat (insucient brine concentration, brine pump failure, blocked brine
Locate and remedy cause of excessively low
temperature in brine circuit. See “Liquid coolers”.
circuit lter, evaporating temperature too low).
Trouble shooting
© Danfoss A/S (AC-DSL/MWA), 10 - 2006 DKRCC.PF.000.G1.02 / 520H1459 173
Fitters notes Trouble shooting - Fault location (Danfoss commercial refrigeration controls)
System fault location (cont.)
Symptom Possible cause Action
Compressor
Will not start.
Compressor runs constantly, suction pressure too low.
Compressor runs constantly, suction pressure too high.
i) Regulating equipment cut out, incorrectly set or
defective: Low-pressure control, Room thermostat.
j) Motor windings burnt out.
1) Open compressor: Compressor and motor overloaded.
Motor undersized.
2) Hermetic and semihermetic compressor: Compressor and motor overloaded.
Acid formation in refrigerant system.
k) Bearing or cylinder seizing because of:
1) Dirt particles in refrigerant system.
2) Copper deposition on machined parts because of acid formation in refrigerant system.
3) Insucient or no lubrication as a result of:
Defective oil pump. Oil boiling in crankcase. Insucient oil. Oil collection in evaporator. Poor or no oil equalisation between
parallel-coupled compressors (oil starvation in compressor started last).
Cut-out pressure of low-pressure control set too low, or defective control.
a) Compressor suction and/or discharge valve not
tight.
b) Compressor capacity too low in relation to load
at any given time.
Locate and repair fault. Start system. See “Suction pressure too low” and page 179. See also pages 175 and 176.
Locate and remedy cause of overload, replace motor.
Replace motor with larger size.
Locate and remedy cause of overload, replace compressor.
Locate and remedy cause of acid formation, remove compressor, clean out refrigerant system if necessary, t new “burn-out” lter, rell with oil and refrigerant, install new compressor.
Clean out system and install new lter drier and new compressor.
Clean out system and install new lter drier and new compressor.
In all circumstances: Locate and remedy the fault, replace defective parts or install new compressor.
See “Compressor, Oil boiling”. See “Compressor, Oil level in crankcase too low”. See “Compressor, Oil level in crankcase too low”. See “Compressor, Oil level in crankcase too low”
See “Suction pressure too low”.
Replace valve plate,
Recommend lower load, or replace compressor with larger size.
174 DKRCC.PF.000.G1.02 / 520H1459 © Danfoss A/S (AC-DSL/MWA), 10 - 2006
Fitters notes Trouble shooting - Fault location (Danfoss commercial refrigeration controls)
Fault location on the thermostatic expansion valve
Symptom Possible cause Remedy
Room temperature too high
Room temperature too high
Refrigeration system hunts Expansion valve superheat set at too small a value. Reset superheat on expansion valve.
Refrigeration system hunts at too high a room tem­perature
Suction pressure too high Liquid ow
Pressure drop across evaporator too high. Replace expansion valve with valve having external
pressure equalization. Reset superheat on expansion valve if necessary.
Lack of subcooling ahead of expansion valve. Check refrigerant subcooling ahead of expansion
valve. Establish greater subcooling.
Pressure drop across expansion valve less than the pressure drop the valve is sized for.
Check pressure drop across expansion valve. Try replacement with larger orice assembly and/or valve. Reset superheat on expansion valve if necessary.
Bulb located to far from evaporator outlet or after an internal heat exchanger or too close to large
Check bulb location. Locate bulb away from large valves, anges, etc.
valves, anges, etc. Expansion valve blocked with ice, wax or other
impurities.
Clean ice, wax or other impurities from the valve. Check sight glass for colour change (green means too much moisture). Replace lter drier if tted. Check oil in the refrig­eration system. Has the oil been changed or replenished? Has the compressor been replaced? Clean the lter.
Expansion valve too small. Check refrigeration system capacity and compare
with expansion valve capacity. Replace with larger valve or orice. Reset superheat on expansion valve.
Charge lost from expansion valve. Check expansion valve for loss of charge.
Replace expansion valve. Reset superheat on expansion valve.
Charge migration in expansion valve. Check whether expansion valve charge is correct.
Identify and remove cause of charge migration. Reset superheat on expansion valve if necessary.
Expansion valve bulb not in good contact with suction line.
Ensure that bulb is secured on suction line. Insulate bulb if necessary.
Evaporator completely or partly iced up. De-ice evaporator if necessary.
Expansion valve capacity too high. Replace expansion valve or orice with smaller size.
Reset superheat on expansion valve if necessary.
Expansion valve bulb location inappropriate, e.g. on collection tube, riser after oil lock, near large valves, anges or similar or after an internal heat exchanger.
Check bulb location. Locate bulb so that it receives a reliable signal. Ensure that bulb is secured on suction line. Set superheat on expansion valve if necessary.
Check refrigeration system capacity and compare Expansion valve too large. Expansion valve setting incorrect.
with expansion valve capacity.
Replace with larger valve or orice.
Reset superheat on expansion valve. Charge lost from expansion valve. Check expansion valve for loss of charge.
Replace expansion valve.
Reset superheat on expansion valve. Charge migration in expansion valve. Increase superheat on expansion valve.
Check expansion valve capacity in relation to
evaporator duty.
Replace expansion valve or orice with smaller size.
Reset superheat on expansion valve if necessary.
Trouble shooting
© Danfoss A/S (AC-DSL/MWA), 10 - 2006 DKRCC.PF.000.G1.02 / 520H1459 175
Fitters notes Trouble shooting - Fault location (Danfoss commercial refrigeration controls)
Fault location on the thermostatic expansion valve (cont.)
Symptom Possible cause Remedy
Suction pressure too low Pressure drop across evaporator too high. Replace expansion valve with valve having
external pressure equalization. Reset superheat on expansion valve if necessary.
Lack of subcooling ahead of expansion valve. Check refrigerant subcooling ahead of expansion
valve. Establish greater subcooling.
Evaporator superheat too high. Check superheat.
Reset superheat on expansion valve.
Pressure drop across expansion valve less than pressure drop valve is sized for.
Bulb located too cold, e.g. in cold air ow or near large valves, anges, etc.
Expansion valve too small. Check refrigeration system capacity and compare
Expansion valve blocked with ice, wax or other impurities.
Charge lost from expansion valve. Check expansion valve for loss of charge.
Charge migration in expansion valve. Check charge in expansion valve.
Check pressure drop across expansion valve. Replace with larger orice assembly and/or valve if necessary.
Check bulb location. Insulate bulb if necessary. Locate bulb away from large valves, anges, etc.
with expansion valve capacity. Replace with larger valve or orice. Reset superheat on expansion valve.
Clean ice, wax and other impurities from valve. Check sight glass for colour change (yellow means too much moisture). Replace lter drier if tted. Check oil in the refrigeration system. Has the oil been changed or replenished? Has the compressor been replaced? Clean the lter.
Replace expansion valve. Reset superheat on expansion valve.
Reset superheat on expansion valve if necessary.
Liquid hammer in compressor
Evaporator wholly or partly iced up. De-ice evaporator if necessary. Expansion valve capacity too large. Replace expansion valve or orice with smaller
size.
Reset superheat on expansion valve if necessary. Superheat on expansion valve set too low. Increase superheat on expansion valve. Expansion valve bulb not in good contact with
suction line. Bulb located too warm or near large valves,
anges, etc.
Ensure that bulb is secured on suction line.
Insulate bulb if necessary.
Check bulb location on suction line.
Move bulb to better position.
176 DKRCC.PF.000.G1.02 / 520H1459 © Danfoss A/S (AC-DSL/MWA), 10 - 2006
Fitters notes Trouble shooting - Fault location (Danfoss commercial refrigeration controls)
Fault location on the solenoid valve
Symptom Possible cause Remedy
Solenoid valve does not open
No voltage on coil Check whether the valve is open or closed
1) use a magnetic eld detector
2) lift the coil and feel whether there is resistance.
NOTE!
Never take the coil o the valve if voltage is applied
- the coil can burn out. Check the wiring diagram and wiring itself. Check relay contacts. Check lead connections. Check fuses.
Incorrect voltage/frequency. Compare coil data with installation data.
Measure operating voltage at the coil. – Permissible variation: 10% higher than rated voltage. 15% lower than rated voltage.
Replace with correct coil if necessary. Burnt-out coil See symptom "Burnt-out coil" Dierential pressure too high Check technical data and dierential pressure of
valve.
Replace with suitable valve.
Reduce dierential. pressure e.g. inlet pressure. Dierential pressure too low Check technical data and dierential pressure of
valve.
Replace with suitable valve.
Check diaphragm and/or piston rings and replace
O-rings and gaskets *)
Replace O-rings and gaskets *) Damaged or bent armature tube Replace defective components *)
Replace O-rings and gaskets *)
Impurities in diaphragm/piston Replace defective components *)
Impurities in valve seat. Impurities in armature/armature
Corrosion/cavitation Replace defective parts *)
Missing components after dismantling valve Fit missing components.
Solenoid valve
Dierential pressure too low Check valve technical data and dierential
opens partially
Damaged or bent armature tube Replace defective components *)
Impurities in diaphragm/piston Clean out impurities.
Impurities in valve seat Impurities in armature/armature tube
Corrosion/cavitation Replace defective parts *)
Missing components after dismantling of valve Fit missing components *)
* See cross section in the instruction. See also the spare parts documentation on http://www.danfoss.com
Replace O-rings and gaskets *)
Clean out impurities.
Replace defective parts *)
Replace O-rings and gaskets *)
Replace O-rings and gaskets *)
Replace O-rings and gaskets *)
pressure. Replace with suitable valve.
Check diaphragm and/or piston rings and replace
O-rings and gaskets *)
Replace O-rings and gaskets *)
Replace defective components *)
Replace O-rings and gaskets *)
Clean out impurities.
Replace defective parts *)
Replace O-rings and gaskets *)
Trouble shooting
Replace O-rings and gaskets *)
Replace O-rings and gaskets *)
© Danfoss A/S (AC-DSL/MWA), 10 - 2006 DKRCC.PF.000.G1.02 / 520H1459 177
Fitters notes Trouble shooting - Fault location (Danfoss commercial refrigeration controls)
Fault location on the solenoid valve (cont.)
Symptom Possible cause Remedy
Solenoid valve does not close/ closes partially
Continuous voltage on coil Lift coil and feel whether there is any resistance.
NOTE!
Never take the coil o if voltage is applied - the coil can burn out. Check the wiring diagram and wiring itself. Check relay contacts. Check lead connec­tions.
Manual spindle not screwed back after use Check spindle position. Pulsation in discharge line. Dierential pressure too
high in open position. Pressure in outlet side sometimes higher than in inlet.
Damaged or bent armature tube Replace defective components *)
Defective valve plate, diaphragm or valve seat Check pressure and ow conditions.
Diaphragm or support plate wrong way round Check for correct valve assembly *)
Impurities in valve plate. Impurities in pilot orice. Impurities in armature tube.
Check technical data of valve. Check pressure and ow condition Replace with suitable valve. Check remainder of system.
Replace O-rings and gaskets *)
Replace defective components *) Replace O-rings and gaskets *)
Replace O-rings and gaskets *)
Clean out impurities. Replace O-rings and gaskets *)
Solenoid valve does not close/ closes partially
Solenoid valve noisy Frequency noise (hum) The solenoid valve is not the cause.
Burnt-out coil
(Coil cold with voltage on)
Corrosion/cavitation of pilot/main orice Replace defective parts *)
Replace O-rings and gaskets *)
Missing components after dismantling of valve Replace missing components *)
Replace O-rings and gaskets *)
Check electrical supply.
Liquid hammer when solenoid valve opens See the chapter “Solenoid valves”
Liquid hammer when solenoid valve closes See the chapter “Solenoid valves”
Dierential pressure too high and/or pulsation in discharge line
Incorrect voltage/frequency Check coil data.
Short-circuit in coil (can be moisture in coil).
Armature will not lift in armature tube a) Damaged or bent armature tube b) Damaged armature c) Impurities in armature tube
Temperature of medium too high Compare valve and coil data installation data.
Ambient temperature too high Change of valve position might be necessary.
Damaged piston, piston rings (on servo-operated solenoid valves type EVRA)
Check technical data of valve. Check pressure and ow conditions. Replace with suitable valve. Check remainder of system.
Replace with correct coil if necessary. Check wiring diagram or wiring itself. Check max. voltage variation.
- Permissible variation: 10% higher than rated voltage 15% lower than rated voltage.
Check remainder of system for short-circuiting. Check lead connections at coil. After remedying fault, replace coil (make sure volt­age is correct). Check O-rings tted on armature tube and inside top nut.
Replace defective components. Clean out impurities *) Replace O-rings and gaskets *)
Replace with suitable valve.
Compare valve and coil data with installation data. Increase ventilation around valve and coil.
Replace defective parts. Replace O-rings and gaskets *)
* See cross section in the instruction. See also the spare parts documentation on http://www.danfoss.com
178 DKRCC.PF.000.G1.02 / 520H1459 © Danfoss A/S (AC-DSL/MWA), 10 - 2006
Fitters notes Trouble shooting - Fault location (Danfoss commercial refrigeration controls)
Fault location on the pressure control
Symptom Possible cause Remedy
High-pressure control disconnected. Warning: Do not start the system before the fault has been located and rectied!
The low-pressure control fails to stop the compressor
Compressor running time too short
Cut-out pressure for KP 7 or KP 17, HP side, does not match the scale value
Dierential spindle on sin­gle unit is bent and the unit does not function
High-pressure control chatters
Condensing pressure too high because: Dirty/clogged condenser surfaces. Fans stopped/water supply failure. Defective phase/fuse, fan motor. Too much refrigerant in system. Air in system.
a) Dierential setting too high so that cut-out pressure falls below –1 bar. b) Dierential setting too high so that compres­ sor cannot pull down to cut-out pressure.
a) Dierential setting on low pressure control too low. b) High-pressure control setting too low, i.e. too close to normal operating pressure. c) Condensing pressure too high because of: Dirty/clogged condenser surfaces. Fans stopped/water supply failure. Defective phase/fuse, fan motor. Too much refrigerant in system. Air in system.
The fail-safe system in the bellows element is activated if the deviations have been greater than 3 bar.
Tumbler action failure arising from attempt to test wiring manually from righthand side of unit.
Liquid-lled bellows multies the damping orice in the inlet connection.
Rectify the stated faults.
Increase the range setting or reduce the dierential.
a) Increase the dierential setting.
b) Check the high-pressure control setting. Increase it if the system data allows.
c) Rectify the stated faults.
Replace the pressure control.
Replace unit and avoid manual test in any way other than that recommended by Danfoss.
Install the pressure control so that liquid cannot collect in the bellows element (see instruction). Eliminate cold air ow around the pressure control. Cold air can create condensate in the bellows element. Fit a damping orice (code no. 060-1048) in the end of the control connection furthest away from the control.
Periodic contact failure
Transition resistance in contacts too high. Fit KP with gold contacts.
on computer-controlled regulation, with minimum voltage and current
© Danfoss A/S (AC-DSL/MWA), 10 - 2006 DKRCC.PF.000.G1.02 / 520H1459 179
Trouble shooting
Fitters notes Trouble shooting - Fault location (Danfoss commercial refrigeration controls)
Fault location on the thermostat
Symptom Possible cause Remedy
Compressor running time too short and temperature in cold room too high
Refrigeration system runs with too high a temperature dierential
Thermostat does not start compressor, even when sensor temperature is higher than the set value. The thermostat does not react to hand-warming of the sensor
Compressor continues to run, even when thermostat sensor is colder than the set value (range setting minus dierential)
Thermostat with absorp­tion charge unstable in operation
Dierential spindle on single unit is bent and the unit does not function
Capillary tube on thermostat with vapour charge touching evaporator, or suction line colder than sensor. a) Reduced air circulation around thermostat sensor. b) Refrigeration system temperature changes so fast that the thermostat can not keep pace. c) Room thermostat mounted on a cold wall in the cold room.
a) Completely or partially lost charge because of fractured capillary tube. b) Part of the capillary tube in a thermostat with vapour charge is colder than the sensor.
A thermostat with vapour charge has been set without taking account of graph curves in the instruction sheet.
Large variation in ambient temperature gives enclosure-sensitivity.
Tumbler action failure arising from attempt to test wiring manually from righthand side of thermostat.
Locate capillary tube so that the sensor is always the coldest part.
a) Find a better sensor location with higher air velocity or better contact with evaporator. b) Use a thermostat with a smaller sensor. Reduce the dierential. Ensure that the sensor has better contact. c) Insulate the thermostat from the cold wall.
a) Replace thermostat and mount sensor/capillary tube correctly. b) Find a better location for the thermostat so that the sensor is always the coldest part. Change to thermostat with adsorption charge.
At low range setting the dierential of the thermostat is larger than indicated in the scale (See diagram in the instruction sheet).
Avoid ambient temperature variations around thermostat. If possible, use a thermostat with vapour charge (not sensitive to ambient temperature variations). Replace thermostat with unit having a larger sensor.
Replace thermostat and avoid manual test in any way other than that recommended by Danfoss.
180 DKRCC.PF.000.G1.02 / 520H1459 © Danfoss A/S (AC-DSL/MWA), 10 - 2006
Fitters notes Trouble shooting - Fault location (Danfoss commercial refrigeration controls)
Fault location on the water valve
Symptom Possible cause Remedy
Condensing pressure too high, water-cooled condensers
Condensing pressure too low, water-cooled condensers
Condensing pressure hunts
WV water valve set for too high a pressure (water quantity too small).
Increase the water quantity by setting the water valve at a lower pressure.
Filter ahead of WV water valve blocked. Clean lter and ush water valve after opening it to
allow full ow (two screwdrivers, see instruction).
Leaking bellows in WV water valve. Check bellows for leakage, using a leak detector
if necessary. Replace bellows element. See spare parts catalogue*. There must be no pressure on bellows element during removal and retting.
Capillary tube between WV water valve and condenser blocked or deformed.
WV water valve closed because of defective upper diaphragm.
Check capillary tube for blockage or deformation. Replace capillary tube.
Check water valve for cracks in diaphragm. Replace diaphragm. See spare parts catalogue*. There must be no pressure on bellows element during removal and retting.
Water quantity too large. Set WV water valve for smaller water quantity, i.e.
higher pressure.
WV water valve open because of defective lower diaphragm.
Check water valve for cracks in diaphragm. Replace diaphragm. See spare parts catalogue*. There must be no pressure on bellows element during removal and retting.
WV water valve cannot close because of dirt in the seat. Valve cone sticks because of dirt.
Check water valve for dirt and clean it. Replace parts as necessary. See spare parts catalogue*. There must be no pressure on bellows element during removal and retting. Install a lter ahead of the water valve.
WV water valve too large. Replace water valve with a smaller size.
*) Find spare part documentation on http://www.danfoss.com
© Danfoss A/S (AC-DSL/MWA), 10 - 2006 DKRCC.PF.000.G1.02 / 520H1459 181
Trouble shooting
Fitters notes Trouble shooting - Fault location (Danfoss commercial refrigeration controls)
Fault location on the lter or sight glass
Symptom Possible cause Action
Sight glass indicator shows yellow
Insucient evaporator capacity
Bubbles in sight glass after lter
Filter outlet side colder than inlet side (can be iced up)
* Rember to seal the old lter after removal.
Too much moisture in system. Replace lter drier*
Pressure drop across lter too high. Compare lter size with system capacity.
Replace lter drier* Filter clogged. Replace lter drier* Filter under-sized. Compare lter size with system capacity.
Replace lter drier* Pressure drop across lter too high. Compare lter size with system capacity.
Replace lter drier* Filter clogged. Replace lter drier* Filter under-sized. Compare lter size with system capacity.
Replace lter drier* Insucient sub-cooling. Check reason for insucient subcooling.
Do not charge refrigerant only because of
insucient sub-cooling.
Insucient refrigerant charge. Charge necessary refrigerant. Pressure drop across lter too high. Compare lter size with system capacity.
Replace lter drier* Filter clogged. Replace lter drier* Filter under-sized. Compare lter size with system capacity.
Replace lter drier*
182 DKRCC.PF.000.G1.02 / 520H1459 © Danfoss A/S (AC-DSL/MWA), 10 - 2006
Fitters notes Trouble shooting - Fault location (Danfoss commercial refrigeration controls)
Fault location on the KV pressure regulator
Symptom Possible cause Action
Room temperature too high
Room temperature too low KVP evaporating pressure regulator set too low. Increase the setting of the evaporating pressure
Suction pressure hunts KVP evaporating pressure regulator too large. Replace evaporating pressure regulator with
Suction pressure too high KVC capacity regulator defective or set too high. Replace capacity regulator. Set capacity regulator
Condensing pressure too high, air-cooled condensers
Condensing pressure too high, water-cooled condensers
Crankcase pressure regulator setting drift
Compressor discharge pipe too hot
Temperature in receiver too high No subcooled liquid
KVP evaporating pressure regulator set too high. Reduce the setting of the evaporating pressure
regulator. The setting should be about 8-10 K lower than required room temperature. Remember to screw on protective cap after nal setting.
Bellows leak in KVP evaporating pressure regulator. Slowly loosen protective cap.
If pressure or traces of refrigerant exist under the cap, there is a leak in the bellows. Replace the valve.
regulator. The setting should be about 8-10 K lower than the required room temperature. Remember to screw on protec­tive cap after nal setting.
smaller size. Remember to screw on the protective cap after nal setting.
KVC capacity regulator too large. Replace capacity regulator with smaller size.
Remember to screw on protective cap after nal setting.
at lower pressure. Remember to screw on protective cap after nal setting.
KVR condensing pressure regulator set too high. Set condensing pressure regulator at correct
pressure. Remember to screw on protective cap after nal setting.
Bellows in KVR condensing pressure regulator might be leaking.
Slowly loosen protective cap. If pressure or traces of refrigerant exist under the cap, there is a leak in the bellows. Replace valve.
Bellows leak in KVL crankcase pressure regulator. Slowly loosen protective cap. If pressure or traces
of refrigerant exist under the cap, there is a leak in the bellows. Replace the valve.
Probable bellows leak in KVC capacity regulator. Slowly loosen protective cap. If pressure or traces
of refrigerant exist under the cap, there is a leak in the bellows. Replace valve.
Hot gas quantity too large. If necessary, set the KVC capacity regulator at
lower pressure. An injection valve (e.g. TE2) can be installed in the suction line.
KVD receiver pressure regulator set for too low a pressure.
Set the receiver pressure regulator at a higher pressure. It might also be necessary to increase the setting of the condensing pressure regulator.
Bellows in KVD receiver pressure regulator might be leaking.
Slowly loosen protective cap. If pressure or traces of refrigerant exist under the cap, there is a leak in the bellows. Replace valve.
Trouble shooting
© Danfoss A/S (AC-DSL/MWA), 10 - 2006 DKRCC.PF.000.G1.02 / 520H1459 183
Fitters notes Trouble shooting - Fault location in refrigeration circuits with hermetic compressors
Contents Page
© Danfoss A/S (AC-DSL/MWA), 10 - 2006 DKRCC.PF.000.G1.02 / 520H1459 185
Trouble shooting
Notes
186 DKRCC.PF.000.G1.02 / 520H1459 © Danfoss A/S (AC-DSL/MWA), 10 - 2006
Fitters notes Trouble shooting - Fault location in refrigeration circuits with hermetic compressors
1.0 Compressor/system does not run (start)
1.1
Main switch drop-out Blown fuse
Short-circuiting to frame Motor defect Defective current lead-in Electrical equipment
Compressor Compressor motor/motor protector mechanically blocked.
Overload Voltage/frequency Pressure irregularity Refrigerant type Pressure equalisation Fan drop-out
High and low-pressure switches Mechanical defect
Incorrect connection Incorrect dierential setting Incorrect cutout setting Pressure irregularity
Thermostat Mechanical defect
Incorrect connection Dierential too small Incorrect cutout value
If the main fuse blows, the cause must be found. This will most often be a defect in the motor windings or motor protector, short-circuiting to frame or a burnt current lead-in which, in turn, causes main fuse drop-out. If a compressor motor refuses to start, always check the resistances rst. All compressors have their main and start windings located as shown in the sketch. Resistance values are stated in the individual data sheets.
1.2
1.3
As a rule, a motor protection is built into all compressor motors. If the winding protector cuts out the motor, due to the heat accumulated in the motor the cut-out period can be relatively long (up to 45 minutes). When the motor will no longer run, resistance measurement will conrm whether a motor protector has cut out or whether a winding is defective. A mechanical seizure in the compressor will show itself by repeated start attempts accompanied by high current consumption and high winding temperatures that cause motor protector cutout.
Compressor overload can be recognised by the compressor refusing to start or by starting and then stopping again after a very short time (via the motor protector). If the com-pressor is used outside its allowed application limits the usual result is overload. Application limits such as voltage tolerances, frequencies, temperature/ pressure and refrige-rant type are given in the individual data sheet. In systems not protected by a high-pressure cut-out switch on the discharge side, a fan motor which is defective or cut out via a motor protector can lead to compressor overload. Generally, the refrigerant quantity must be determined precisely. In capillary tube systems the most certain method is to take temperature measurements on the evaporator and suction line.
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Fitters notes Trouble shooting - Fault location in refrigeration circuits with hermetic compressors
1.4
1.5
In systems with thermostatic expansion valve, charging must be checked using a sight glass. In both systems, the refrigerant quantity must be less than the quantity that can be accommodated in the free volume on the discharge side.
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Compressors for capillary tube systems are usually equipped with a PTC LST starting device. Starting via a PTC requires complete pressure equalisation between the high and low-pressure sides on every start. In addition, before it can operate, the PTC requires a standstill time of about 5 minutes to ensure that the PTC component is cooled down in order to achieve maximum starting torque. When a “cold” compressor is started and the current is cut o a short time after, conict can arise between the PTC and the motor protector. Because the motor retains heat, up to approx. 1 hour can elapse before normal start is possible.
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1.6
1.7
1.8
In systems where pressure equalisation on starting is not certain, the compressor must be equipped with an HST starting device. This also applies to capillary tube systems with a standstill time of less than 5 minutes. Defective or incorrect relays and starting capacitors can cause starting problems or that the compressor is cut out via the motor protector. Note the manufacturer’s compressor data. If the starting device is thought to be defective the whole equipment must be replaced, including the relay and starting capacitor.
The PTC (25 Ω for 220 V mains and approx. 5 Ω for 115 V mains) can be checked using an ohmmeter.
A starting relay can be checked with a lamp, see sketch. The relay is in order if the lamp does not light up when the relay is upright. The relay is also in order if the lamp lights up when the relay is upside down.
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Fitters notes Trouble shooting - Fault location in refrigeration circuits with hermetic compressors
1.9
1.10
A starting capacitor can also be checked by applying rated mains voltage to it for a few seconds and then short-circuiting the leads. If sparks appear, the capacitor is in order.
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In some markets, Danfoss oers condensing units with combined high and low-pressure switches that protect the compressor against excessive pressure on the discharge side and too low pressures on the suction side. If the high-pressure switch has cut out the system, a check should be made to see whether pressure irregularity is occurring. If the low-pressure switch has cut out, the cause can be insucient refrigerant amount, leakage, evaporator icing and/or partial blockage of the throttling device. If there is no pressure irregularity on the high or low-pressure sides, the pressure switch itself must be checked. See also the chapter “Pressure controls”.
1.11
The system can also cut out because of a defective or incorrectly set/sized thermostat. If the thermostat loses charge or if the temperature setting is too high, the system will not start. If the temperature dierential is set too low, compressor standstill periods will be short and there might be starting problems with an LST starting device and shortened compressor life with an HST starting device. The guideline for pressure equalisation time using an LST starting device is 5 to 8 minutes for refrigerators and 7 to 10 minutes for freezers.
If an HST starting device is used, the aim is to keep the cut-in periods per hour as few as possible. Under no circumstances must there be more than ten starts per hour. See also the chapter “Thermostats”.
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Fitters notes Trouble shooting - Fault location in refrigeration circuits with hermetic compressors
2.0 The compressor/system runs, but with reduced refrigeration capacity
2.1
2.2
Compressor Leakage
Pressure irregularity Blockage
Throttling device Capillary tube/thermostatic expansion valve
Coking
Non-condensible gases Moisture Dirt Fan defect Refrigerant loss Refrigerant overcharge Icing
Static superheat setting Orice size/diameter
Frequent causes of reduced refrigeration capacity are coking, and copper plating which lead to reduced life time of the compressor and burst gaskets in the compressor valve system. Coking occurs mainly as a result of moisture in the refrigeration system. In high temperatures, the presence of moisture also causes copper plating on valve seats. The burst gaskets are the result of an excessive condensing pressure and excessively high short-lived pressure peaks >60 bar (liquid hammer).
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We recommend the installation of good quality lter driers. If the lter material is of poor quality, wear will occur which will not only cause the partial blockage of capillary tube and the lter in the thermostatic expansion valve, but it will also damage the compressor (mainly seizure).
2.3
2.4
In general, commercial refrigeration systems must be equippd with lters having a solid core, e.g. type DML. See also the chapter “Filter driers & sight glasses”. The lter drier must be replaced after every repair. When replacing a “pencil drier” (often used in refrigerators) care must be taken to ensure that the lter material used is suitable for the refrigerant and that there is sucient material for the application.
Poorly soldered joints can also cause system blockage. Making good soldered joints is conditional on using the correct soldering metal containing the correct percentage of silver. The use of ux should be limited and kept to as minimum as possible.
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Fitters notes Trouble shooting - Fault location in refrigeration circuits with hermetic compressors
2.5
2.6
Poorly soldered joints can also cause leakage and thereby coking. In a refrigeration circuit the proportion of non-condensible gases should be kept below 2%, otherwise the pressure level will rise. The main purpose of evacuation is to remove non-condensible gases before the refrigerant is charged. This also produces a drying eect in the refrigeration system. Evacuation can be performed either from both discharge and suction sides, or from the suction side only. Evacuation from both sides gives the best vacuum. Evacuation from the suction side only makes it dicult to obtain sucient vacuum on the discharge side. Therefore, with one­sided evacuation, intermediate ushing with dry Nitrogen is recommended until pressure equalisation is achieved.
Dirt on the condenser and a fan motor defect can cause excessive condensing pressure and thereby reduced refrigeration capacity. In such cases the built-in high-pressure switch provides overload protection on the condenser side. Note: The built-in motor protector does not give the compressor optimum protection if the condensing pressure rises as a result of a fan motor drop-out. The temperature of the motor protector does not rise quickly enough to ensure the protector cutout. This also applies when the refrigerant quantity is greater than can be accommodated in the free volume on the discharge side.
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2.7
2.8
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It is important to determine the quantity of refrigerant precisely – especially in capillary tube systems. The guidelines are that the temperature on the evaporator inlet must, as far as possible, be the same as the temperature at its outlet, and that as much superheating as possible must be obtained between the evaporator outlet and the compressor inlet. (The inlet temperature on the compressor must be about 10 K less than the condensing temperature).
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Overcharging of a refrigeration system equipped with a thermostatic expansion valve becomes critical when the charging quantity in liquid condition is greater than can be accommodated by the free volume in the receiver, i.e. the condenser area is reduced and the condensing pressure rises.
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Fitters notes Trouble shooting - Fault location in refrigeration circuits with hermetic compressors
2.9
2.10
It is very seldom that there is too little refrigerant in a system, unless leakage occurs. Irregular icing on the evaporator is often a sign of insucient refrigerant. This irregular icing does not only reduce the refrigeration output, it can also give problems in evaporator defrosting because the defrost thermostat sensor does not register the presence of ice. Therefore, precise determination of the refrigerant charge is recommended as a way of making sure that ice on the evaporator is evenly distributed.
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The optimum system eciency is obtained when a heat exchanger is tted to ensure subcooling: about 5 K in systems with thermostatic expansion valve and about 3 K in systems with capillary tube. In systems with a thermostatic expansion valve the suction and liquid lines must be soldered together over a distance of 0.5 to 1.0 m. In capillary tube systems the capillary tube and suction line must be soldered together for 1.5 to
2.0 m.
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Fitters notes Trouble shooting - Fault location in refrigeration circuits with hermetic compressors
3.0 Power consumption too high
3.1
Compressor Signs of compressor wear
Pressure irregularity Blockage
Overload Application limits exceeded
Motor defect Reduced refrigeration capacity Compressor cooling
Non-condensible gases Moisture Dirt Fan defect
Voltage/frequency Pressure irregularity Temperature Refrigerant type
Pressure irregularity and overload often cause compressor defects that show themselves in the form of increased power consumption. Refer to the previous pages for information on problems with pressure irregularity and compressor overload seen from the system side. Excessive evaporating and condensing pressures cause compressor motor overload which leads to increased power consumption. This problem also arises if the compressor is not suciently cooled, or if extreme overvoltage occurs. Undervoltage is not normally a problem in Western Europe because here the voltage rarely drops below 198 V.
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3.2
3.3
Constant overload will give signs of wear in compressor bearings and valve systems. Overload that causes frequent winding protector cutouts can also produce an increased number of electrical drop-outs. In cases where the application limits are exceeded, the system must be adapted. For example, by the use of a thermostatic expansion valve with an MOP that will limit the evaporating pressure, a pressure regulator, or a condensing pressure regulator. See also the chapter “Thermostatic expansion valves” and the chapter “Pressure regulators”.
Static cooling (in certain circumstances an oil cooler) is sucient for most household refrigeration appliances, provided that the clearances specied by the manufacturer are maintained, especially where a built-in appliance is concerned.
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Fitters notes Trouble shooting - Fault location in refrigeration circuits with hermetic compressors
3.4 Commercial equipment should be fan-cooled.
The normal recommended air velocity across condenser and compressor is 3 m/s.
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3.5
A further recommendation is regular service on the refrigeration system, including cleaning of the condenser.
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Fitters notes Trouble shooting - Fault location in refrigeration circuits with hermetic compressors
4.0 Noise
4.1
Compressor Pressure circuit
Oil level Clearance: piston/cylinder Valve system
Fan Deformed fan blades
Bearing wear Baseplate
Valves Whistling« from thermostatic expansion valves
»Chatter« from solenoid and check valves
System noise Liquid noise
(mainly in evaporator)
Installation Piping
Compressor, fan and condenser brackets
Danfoss compressors and condensing units do not normally give rise to complaints about noise. The noise level of compressors and, above all, fans is well in agreement with the demands made by the market. If occasional complaints are received, they usually arise from installation or system errors.
4.2
4.3
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The rare noise problems that do occur are mostly because of production faults, e.g. discharge line touching the compressor housing, oil level too high/low, too much clearance between piston and cylinder, faulty assembly of the valve system. Such noise is easy to diagnose with a screwdriver used as a "stethoscope".
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System noise is a critical factor in household appliances. Here, liquid noise at the evaporator inlet is characteristic. On the system side it is dicult to remedy this problem because what is involved is a mass produced equipment. If the lter is mounted vertically, it might help to mount it horizontally instead. However, it should be remembered that noise can be amplied by structure, e.g. with a built-in appliance. In such a situation, the manufacturer should be contacted.
Trouble shooting
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Fitters notes Trouble shooting - Fault location in refrigeration circuits with hermetic compressors
4.5
4.6
To prevent noise transfer, pipework should not be allowed to touch the compressor, the heat exchanger or the side walls. When installing a compressor, the ttings and grommet sleeves supplied must be used to avoid the rubber pads being compressed so much that they lose their noise-suppression properties.
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Fans are used mostly in commercial refrigeration systems. Noise will be generated if the fan blades become deformed or touch the heat exchanger ns. Worn bearings also produce a great deal of noise. Additionally, the fan unit must be rmly secured so that it does not move in relation to its mounting bracket. Normally, fans have a higher noise level than compressors. In some circumstances, it is possible to reduce the noise level by installing a smaller fan motor, but this can only be recommended when the condenser area is over-sized.
4.7
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If the noise comes from the valves, the cause is usually incorrect sizing. Solenoid and check valves must never be sized to suit the pipe connections, but in accordance with the kv value. This ensures the min. pressure drop necessary to open the valve and keep it open without valve "chatter". Another phenomenon is "whistling" in thermostatic expansion valves. Here a check should be made to ensure that the size of the orice corresponds to the system characteristics and that above all there is sucient liquid sub­cooling ahead of the expansion valve [approx. 5 K].
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Fitters notes Trouble shooting - Fault location overview (Danfoss compressors)
Contents Page
Fault location (Most common fault reasons, detectable before dis-mounting compressor) . . . . . . . . . 202
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Notes
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Fitters notes Trouble shooting - Fault location overview (Danfoss compressors)
General
This section is directed especially to the service network, for household appliances and similar. It deals mainly with PL, TL, NL and FR compressors for 220-240V. For detailed information on compressors see the data sheets.
Compressors type PL, TL, NL, FR and partly SC are equipped with a PTC starting device (g. 1) or a relay and start capacitor (g. 2). The motor protector is built into the windings.
In the event of a start failure, with a cold compressor, up to 15 minutes can elapse before the protector cuts out the compressor.
When the protector cuts out and the compressor is warm, it can take up to 1 hour before the protector cuts in the compressor again.
The compressor must not be started without the electrical equipment.
Fig. 1: PTC starting device
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Fig. 2: Starting relay
Fault location
Electrical compressor quick check
Before beginning systematic fault location, a good rule is to cut the supply voltage for at least 5 minutes. This ensures that the PTC starting device has cooled o and is ready for start.
A voltage drop or blackout within the rst minutes of a pull down of the appliance with cold compressor, can lead to an interlocking situation.
To avoid unneccessary protector operation and consequent waiting time, it is important to carry out fault location in the sequence given below. Tests are made according to desriptions on following page.
Remove electrical equipment Check electrical connection between main
and start pins of compressor terminal Check electrical connection between main
and common pins of Compressor terminal Replace compressor, if above connection
checks failed Else, replace electrical equipment
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A compressor with PTC can not start at non equalized pressure and the PTC does not cool down so fast. It can take more than 1 hour until the appliance then operates normally again.
If the compressor still does not operate, most probably it is no electrical compressor failure. For more detailed fault location, see the tables.
Trouble shooting
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Fitters notes Trouble shooting - Fault location overview (Danfoss compressors)
Check main and start winding
Resistance between pins M (main) and S (start) on compressor terminals is measured with an ohm-meter, see g. 3.
Connection → Main and start windings normally OK → Replace relay No connection → Main or start winding defective → Replace compressor
At cold compressor (ca. 25°C) the values are ca. 10 to 100 Ohm for 220-240 V compressors. For partial short circuit detection, exact values are needed from data sheets of the specic compressor, which can be found on the Danfoss Compressors homepage.
Fig. 3: Compressor terminals Fig. 4: Windings and protector
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Check protector
Resistance between pins M (main) and C (common) on compressor terminals is measured with an ohm-meter, see g. 3 and 4.
Connection → Protector OK No connection → Compressor cold → Protector defective → Replace compressor
Compressor hot → Protector could be OK, but cut out → Wait for reset
Check relay Remove relay from compressor.
Measure connection between connectors 10 and 12 (see g. 5):
No connection → Relay defective → Replace relay
Measure connection between connectors 10 and 11:
In normal vertical position (like mounted, solenoid upward):
Connection → Relay defective → Replace relay No connection → OK
In top-down position (solenoid downward):
Connection → OK No connection → Relay defective → Replace relay
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Fitters notes Trouble shooting - Fault location overview (Danfoss compressors)
Check PTC
Remove PTC from compressor. Shake by hand. Pin C can slightly rattle.
Internal rattle noise (except pin C) →
PTC defect → Replace PTC
Measure resistance between pins M and S, see g. 6.
Resistance value between 10 and 100 Ohm at room temperature for 220 V PTC.
Connection → PTC working → OK No connection → PTC defect → Replace PTC
Fig. 5: Relay connections Fig. 6: PTC connections (backside)
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Fitters notes Trouble shooting - Fault location overview (Danfoss compressors)
Fault location
Most common fault reasons, detectable before dis-mounting compressor.
Customer claim
No/reduced cooling
First analysis
Compressor does not run
Compressor runs 100%
Possible cause
Compressor gets no or bad power supply
Defective relay
Defective start cap PTC defective
Compressor with PTC can not start at pressure difference PTC defective
Relay defective
Compressor overloaded
Defective motor windings Defective protector Mechanically blocked compressor
No or low refrigerant charge
Check
Voltage at plug and fuse Aplicance energized Thermostat function Cables and connections in appliance Voltage at compressor terminals Relay function by shaking to hear if armature is working Start capacitor function PTC by shaking PTC resistance 10 to 100 Ohm between M and S pin Stop time long enough for pressure equalization
PTC resistance 10 to 100 Ohm between M and S pin Relay function by shaking, to hear moving of armature Condenser pressure and ventilation Ambient temperature too high according to type label of appliance Check winding resistances
Check protector with ohmmeter Start with proper starting equipment, voltage and conditions, windings and protector OK Recharge and search for leaks
Activity (depends on result)
Replace relay
Replace start capacitor Replace if noise appears Replace PTC, if not 10 to 100 Ohm Adjust thermostat difference
Replace PTC
Replace relay and capacitor
Ensure proper ventilation
Replace compressor
Replace compressor Replace compressor
Ensure leakfree system and proper charge
Compressor runs on/off
Too high ambient temperature Too high condensing temperature Capillary partly blocked
Valves coked or damaged
Thermostat not OK Wrong refrigerant charge
Ice block built up on evaporator
Compressors trips on motor protector
Ambient temperature according to type label of appliance Condenser and compressor ventilation
Recharge and search for leaks, measure suction pressure. Capillary blocked, if pressure very low Recharge and search for leaks
Thermostat type and function Recharge and search for leaks
Check for ice on evaporator Thermostat function and settings Internal no-frost fan function Compressor load, compressor and condenser ventilation Compressor voltage supply for minimum 187 V Compressor voltage supply for drop outs. Check thermostat and appliance cables for loose connections Motor windings resistance for partly short circuit or earth connection
Replace drier
Ensure proper ventilation and wall distance
Replace compressor, if still not cooling properly Replace thermostat Ensure leakfree system and proper charge, Replace drier Defrost properly Replace thermostat Ensure proper ventilation and wall distance Ensure proper power supply
Fix all connections
Replace compressor
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Fitters notes Trouble shooting - Fault location overview (Danfoss compressors)
Fault location
(continued)
Customer claim
Noise
Fuses are blown by appliance
First analysis
Rattle or humming
Banging at start or stop of compressor
Relay clicking frequently after start
Short circuit in appliance
Short circuit in compressor
Fuse blows at compressor start
Starting capacitor exploded
Starting relay cap blown off
Possible cause
Tube touching cabinet
Compressor touching cabinet Broken internal suspension spring or discharge tube
Resonance Fan noise
Compressor block hitting housing internally
Compressor over­loaded
Relay defective Defective cabling in appliance Defective thermostat Ground connection Defective terminals
Short circuit between cables at terminals Short circuit in compressor motor Supply voltage too low Fuse loaded by too many appliances Resettable fuse too quick acting Partly short circuit to earth
Defective relay
Wrong relay type Extremely many starts and stops of compressor Short circuit in compressor motor
Check
Tube placing
Compressor mounting and rubber feet
Listen to compressor with screw-driver against compressor with edge and to your ear with grip Find vibrating mounting parts Vibration of fan or fan mounting
Compressor overload by pressure
Fan function Refrigerant charge Pressure equalization before start and num­ber of on/off cycles Ambient temperature according to type label Ventilation to compressor and condenser. Check fan function
Right relay type for compressor All connecting cables and power supply cord for loose connections, short circuits Thermostat connections Resistance from line/neutral to earth For burns on the terminal pins
Connectors and cables at compressor
Resistance values in windings Resistance between terminals and earth Supply voltage at compresor start >187 V Total fuse load
Fuse load and type
Resistance between terminals and earth
Relay function by shaking, to hear moving of armature Relay type Relay type Thermostat defect or differences too small Compressor motor resistances
Activity (depends on result)
Bend tube to their right place, carefully Place rubber feet and mounting accessories correctly Replace compressor, if abnor­mal sounds
Place or fix correctly Fix fan and blade, replace, if defective Clean condenser if dusty. Make sure, that ventilation gaps for air circulation are satisfactory
Recharge, if too high Adjust thermostat, if stop time less than 5 min Take appliance out of function, if ambient too hot Clean condenser if dusty. Make sure, that ventilation gaps for air circulation are satisfactory Replace relay, if wrong Fix connections properly
Fix connections properly
Replace electrical accessories Insulate cables and connectors Replace compressor, if short circuited
Connect applaince to different fuse If possible replace by slightly slower type Replace compressor, if short circuited Replace relay and capacitor
Replace relay and cap Replace relay and cap Adjust or replace thermostat Replace compressor
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Trouble shooting
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