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Measuring instruments
Service guide
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Danfoss Measuring instruments Service guide

Fitters notes Trouble shooting
Page
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
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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.
Ae0_0010
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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
Ae0_0015
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Fitters notes Trouble shooting - Measuring instruments
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.
Ae0_0034
Ae0_0016
158 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 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
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