Danfoss Measuring instruments Service guide

Fitters notes	Trouble shooting

This chapter is divided into four sections:	Page
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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Fitters notes	Trouble shooting - Measuring instruments
Contents		Page
	Measuring Instruments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	149
	Instruments for fault location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	149
	Classification 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
Measuring Instruments	The items of equipment most often used for
Instruments for fault location	locating faults in refrigeration systems are as		90
	follows:
	1.	Pressure gauge
	2.	Thermometer
	3.	Hygrometer
	4.	Leak detector
	5.	Vacuum gauge
	6.	Clamp ammeter
	7.	Megger
	8.	Pole finder
			Ae0_0045

Classification of instruments Instruments for fault location and servicing on refrigeration systems should fulfil 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.

CLASS N 1

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a. Uncertainty	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

b. Resolution	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	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.

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e. Temperature stability	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.

Electronic instruments	Electronic instruments can be sensitive to humi-
	dity.
	Some can be damaged by condensate if ope-
	rated 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.

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Ae0_0005

Check and adjustment	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.

Ae0_0006

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Fitters notes

Trouble shooting - Measuring instruments

Check and adjustment (cont.) The proper final inspection and adjustment of instruments can be performed by approved test institutions.

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Adjustment and calibration

Pressure gauges

Service pressure gauges

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.

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.

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Ae0_0009

Vacuum gauges	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	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 varia-
	tions with this type of thermometer.

Ae0_0011

	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 fill 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 recog-
	nised test institute.
Hygrometer	There are different 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.

Ae0_0013

Ae0_0014

At low temperature and high humidity, the temperature differential 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.

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
	Faults on refrigeration systems, general . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	157
	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 effect on the system operation . . . . . . . . . . . . . . . . . . . . . .	. 159
	Visible faults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	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 effect on the system operation . . . . . . . . . . 162
	Faults that can be felt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 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
	Refrigeration system with two air coolers and air-cooled condenser . . . . . . . . . . . . . . .	164
	Refrigeration system with liquid cooler and water-cooled condenser . . . . . . . . . . . . . .	. 165
	Guide to fault location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	. 166
	System fault location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	167
	Fault location on the thermostatic expansion valve . . . . . . . . . . . . . . . . . . . . . . .	175
	Fault location on the solenoid valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	177
	Fault location on the pressure control . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	. 179
	Fault location on the thermostat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	180
	Fault location on the water valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	181
	Fault location on the filter or sight glass . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	182
	Fault location on the KV pressure regulator . . . . . . . . . . . . . . . . . . . . . . . . . . .	<![if ! IE]> <![endif]>shootingTrouble
		183
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Notes

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Fitters notes	Trouble shooting - Fault location (Danfoss commercial refrigeration controls)
Faults on refrigeration	This booklet deals with common faults in small,
systems, general	relatively simple refrigeration systems.
	The faults, fault causes, remedies and effects 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

Fault location without the use of instruments

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.

Ae0_0012

Categorisation	This booklet is divided into two sections. The
	first section deals exclusively with faults that
	can be observed directly with the senses. Here,
	symptoms, possible causes and the effect 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

Knowledge of the system is	An important element in the fault location
required	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 influence 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 briefly at

the most important instruments used in fault location.

In the following description of faults in refrigeration systems, sections 1 and 2 take as their starting points the piping diagrams, fig. 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_0034

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Fitters notes	Trouble shooting - Fault location (Danfoss commercial refrigeration controls)

Visible faults and the effect on the system operation Text in [ ] indicates fault cause

	Visible faults		Effect 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]	- Increased condensing pressure.
	b)	Fan stopped.	- Reduced refrigeration output.
			- Increased energy consumption.
		[Motor defect]
			For an air-cooled condenser, the difference between air inlet
		[Motor protector cut-out]
			and condensing temperatures should lie between 10 K and 20 K,
	c) Fan rotates in wrong direction.
			preferably at the lower end.
		[Installation error]
	d)	Fan blades damaged.
	e)	Fins deformed
		[Rough treatment]
	Water-cooled condenser		For a water-cooled condenser, the difference between condensing
	with sight glass: See “Receiver”.		and water inlet temperatures should lie between 10 K and 20 K,
			preferably at the lower end.
	Receiver with sight glass
	Liquid level too low.
		[Insufficient 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.
			Low suction pressure or compressor cycling.
	Liquid line
	a)	Too small	Faults under a), b) and c) cause:
		[Sizing error]	Large pressure drop in liquid line.
	b)	Too long	Vapour in liquid line.
		[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]	thermostatic expansion valve.
	b)	Brown	Risk of wear in moving parts and blockage in valves and filters.
		[Dirt particles in system]
	c) Pure vapour in sight glass.		Standstill via low-pressure control or compressor cycling.
		[Insufficient liquid in system]
		[Valve in liquid line closed]	Standstill via low-pressure control.
		[Complete blockage, e.g. of filter drier]	Standstill via low-pressure control.
	d) Liquid and vapour bubbles in sight glass.		All faults under d):
		[Insufficient liquid in system]	Compressor cycling or running at low suction pressure.
		[Valve in liquid line partly closed]
		[Partial blockage, e.g. of filter drier]
		[No subcooling]

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Fitters notes		Trouble shooting - Fault location (Danfoss commercial refrigeration controls)
Visible faults and the effect on the system operation (cont.)			Text in [ ] indicates fault cause
Visible faults			Effect on system operation
Thermostatic expansion valve
a)	Thermostatic expansion valve heavily frosted, frost on		Faults under a) cause operation at low suction pressure or
	evaporator only near valve.		compressor cycling via low-pressure control.
	[Dirt strainer partly blocked]
	[Bulb charge partly lost]
	[Previously described faults causing vapour bubbles in
	liquid line]
b)	Thermostatic expansion valve without external pressure		Faults under b), c) cause operation at low suction pressure or
	equalisation, evaporator with liquid distributor.		compressor cycling via low-pressure control. or compressor
	[Sizing or installation error]		cycling via low-pressure control.
c)	Thermostatic expansion valve with external pressure
	equalisation, equalising tube not mounted.
	[Installation error]
d)	Bulb not firmly secured.		Faults under d), e), f) lead to overcharged evaporator with risk of
	[Installation error]		liquid flow to compressor and compressor damage.

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		Faults under a) cause:
		valve heavily frosted.	High superheat at evaporator outlet and operation at mostly low
		[Thermal valve fault]	suction pressure.
		[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]	- Operation with mostly low suction pressure.
	c) Fan does not run.		- Reduced refrigeration output.
			- Increased energy consumption.
		[Motor defect or motor protector cut-out]
			For thermostatic expansion valve controlled evaporators:
	d)	Fan blades defective.
			The difference between air inlet and evaporating temperatures
	e)	Fins deformed.
			should lie between 6 K and 15 K, preferably at the lower end.
		[Rough treatment]
			For level-controlled evaporators:
			The difference between air inlet and evaporating temperatures
			should lie between 2 K and 8 K, preferably at the lower end.
	Liquid cooler
	a) Thermostatic expansion valve bulb not firmly secured.		Causes overcharged evaporator with risk of liquid flow to
		[Installation error]	compressor and compressor damage.
	b) Thermostatic expansion valve without external pressure		Faults b), c) cause:
		equalising on liquid cooler with high pressure drop, e.g.	- Operation with mostly low suction pressure.
		coaxial evaporator.	- Reduced refrigeration output.
		[Sizing or installation error]	- Increased energy consumption.
	c) Thermostatic expansion valve with external pressure		For thermostatic expansion valve controlled evaporators:
		equalisation, equalising tube not mounted.
			The difference between air inlet and evaporating temperatures
		[Installation error]
			should lie between 6 K and 15 K, preferably at the lower end.
			For level-controlled evaporators:
			The difference between air inlet and evaporating temperatures
			should lie between 2 K and 8 K, preferably at the lower end.

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Fitters notes	Trouble shooting - Fault location (Danfoss commercial refrigeration controls)

Visible faults and the effect on the system operation (cont.) Text in [ ] indicates fault cause

Visible faults		Effect on system operation
Suction line
a)	Abnormally severe frosting.	Risk of liquid flow 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 flow to compressor and compressor damage.
	[Thermal valve superheat too low]
Compressor
a) Dew or frost on compressor inlet side.		Liquid flow to compressor with risk of compressor damage.
	[Superheat at evaporator outlet too low]
b) Oil level too low in crankcase.
	[Insufficient oil in system]	System stop via oil differential pressure control (if fitted).
	[Oil collection in evaporator]	Causes wear of moving parts.
c) Oil level too high in crankcase.
	[Oil overfilling]	Liquid hammer in cylinders, risk of compressor damage:
	[Refrigerant mixed with oil in too cold a compressor]	- Damage to working valves.
	[Refrigerant mixed with oil because superheat too low	- Damage to other moving parts.
		- Mechanical overload.
	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	Liquid hammer, damage as under c)
	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 floor.
	[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.

© Danfoss A/S (AC-DSL/MWA), 10 - 2006

DKRCC.PF.000.G1.02 / 520H1459

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Fitters notes	Trouble shooting - Fault location (Danfoss commercial refrigeration controls)

Faults that can be felt, heard or smelled and the effect on the system operation

Text in [ ] indicates fault cause

Faults that can be felt	Effect 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 filter.
[Filter partly blocked with dirt on inlet side]	Vapour in liquid line.
Faults that can be heard	Effect 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	Effect on system operation
Cold room
Bad smell in meat cold room.
[Air humidity too high because evaporator too large or	Leads to poor food quality and/or wastage.
load too low]

162

DKRCC.PF.000.G1.02 / 520H1459

© Danfoss A/S (AC-DSL/MWA), 10 - 2006