Fitters notes |
Trouble shooting |
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This chapter is divided into four sections: |
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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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<![if ! IE]> <![endif]>shooting Trouble |
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Fitters notes |
Trouble shooting - Measuring instruments |
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Contents |
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Page |
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Measuring Instruments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
149 |
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Instruments for fault location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
149 |
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Classification of instruments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
. 149 |
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a. Uncertainty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
. 149 |
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b. Resolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
149 |
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c. Reproducibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
150 |
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e. Temperature stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
150 |
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Electronic instruments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
. 150 |
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Check and adjustment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150 |
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Adjustment and calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
151 |
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Pressure gauges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
. 151 |
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Service pressure gauges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151 |
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Vacuum gauges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151 |
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Thermometer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152 |
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Hygrometer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
. 152 |
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<![if ! IE]> <![endif]>shooting Trouble |
© Danfoss A/S (AC-DSL/MWA), 10 - 2006 |
DKRCC.PF.000.G1.02 / 520H1459 |
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Notes
148 |
DKRCC.PF.000.G1.02 / 520H1459 |
© Danfoss A/S (AC-DSL/MWA), 10 - 2006 |
Fitters notes |
Trouble shooting - Measuring instruments |
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Measuring Instruments |
The items of equipment most often used for |
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Instruments for fault location |
locating faults in refrigeration systems are as |
90 |
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follows: |
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1. |
Pressure gauge |
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2. |
Thermometer |
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3. |
Hygrometer |
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4. |
Leak detector |
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5. |
Vacuum gauge |
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6. |
Clamp ammeter |
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7. |
Megger |
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8. |
Pole finder |
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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
Ae0_0046
a. Uncertainty |
The uncertainty (accuracy) of an instrument is the |
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accuracy with which it is able to give the value of |
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the measured variable. |
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Uncertainty is often expressed in % (±) of |
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either: Full scale (FS) or the measuring value. |
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An example of uncertainty for a particular |
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instrument is ±2% of measuring value, i.e. less |
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uncertain (more accurate) than if the uncertainty |
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is ±2% of FS. |
Ae0_0047
b. Resolution |
The resolution of an instrument is the smallest |
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unit of measurement that can be read from it. |
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For example, a digital thermometer that shows |
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0.1°C as the last digit in the reading has a |
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resolution of 0.1°C. |
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Resolution is not an expression of accuracy. Even |
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with a resolution of 0.1°C, an accuracy as poor as |
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2 K is not uncommon. |
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It is therefore very important to distinguish |
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between the two. |
Ah0_0006
© Danfoss A/S (AC-DSL/MWA), 10 - 2006 |
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Troubleshooting 149
Fitters notes |
Trouble shooting - Measuring instruments |
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c. Reproducibility |
The reproducibility of an instrument is its ability |
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to repeatedly show the same result for a constant |
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measuring value. |
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Reproducibility is given in % (±). |
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d. Long-term stability |
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Long-term stability is an expression how much |
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the absolute accuracy of the instrument changes |
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in, say, one year. |
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Long-term stability is given in % per year. |
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Ae0_0003
e. Temperature stability |
The temperature stability of an instrument is how |
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much its absolute accuracy changes for each °C |
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temperature change the instrument is exposed |
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to. |
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Temperature stability is given in % per °C. |
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Knowledge of the temperature stability of the |
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instrument is of course important if it is taken |
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into a cold room or deep freeze store. |
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Electronic instruments |
Electronic instruments can be sensitive to humi- |
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dity. |
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Some can be damaged by condensate if ope- |
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rated immediately after they have been moved |
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from cold to warmer surroundings. |
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They must not be operated until the whole |
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instrument has been given time to assume the |
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ambient temperature. |
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Never use electronic equipment immediately |
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after it has been taken from a cold service vehicle |
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into warmer surroundings. |
Ae0_0004 |
Ae0_0005 |
Check and adjustment |
Readings from ordinary instruments, and perhaps |
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some of their characteristics, change with time. |
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Nearly all instruments should therefore be |
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checked at regular intervals and adjusted if |
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necessary. |
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Simple checks that can be made are described |
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below, although they cannot replace the kind of |
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inspection mentioned above. |
Ae0_0006
150 |
DKRCC.PF.000.G1.02 / 520H1459 |
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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.
Ae0_0007
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.
Ae0_0008
Ae0_0009
Vacuum gauges |
Vacuum gauges are used in refrigeration to |
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measure the pressure in the pipework during and |
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after an evacuation process. |
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Vacuum gauges always show absolute pres-sure |
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(zero point corresponding to absolute vacuum). |
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Vacuum gauges should not normally be exposed |
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to marked overpressure and should therefore be |
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installed together with a safety valve set for the |
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maximum permissible pressure of the vacuum |
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gauge. |
Ae0_0010
© Danfoss A/S (AC-DSL/MWA), 10 - 2006 |
DKRCC.PF.000.G1.02 / 520H1459 |
Troubleshooting 151
Fitters notes |
Trouble shooting - Measuring instruments |
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Thermometer |
Electronic thermometers with digital read-out |
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are in widespread use for servicing. Examples of |
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sensor versions are surface sensors, room sensors |
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and insertion sensors. |
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Thermometer uncertainty should not be greater |
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than 0.1 K and the resolution should be 0.1°C. |
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A pointer thermometer with vapour charged |
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bulb and capillary tube is often recommended for |
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setting thermostatic expansion valves. |
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As a rule it is easier to follow temperature varia- |
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tions with this type of thermometer. |
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Ae0_0011
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Thermometers can be relatively easily checked |
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at 0°C in that the bulb can be inserted 150 to 200 |
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mm down into a thermos bottle containing a |
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mixture of crushed ice (from distilled water) and |
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distilled water. The crushed ice must fill the whole |
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bottle. |
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If the bulb will withstand boiling water, it can |
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be held in the surface of boilover water from |
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a container with lid. These are two reasonable |
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checks for 0°C and 100°C. |
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A proper check can be performed by a recog- |
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nised test institute. |
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Hygrometer |
There are different types of hygrometers for |
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measuring the humidity in cold rooms and air |
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conditioned rooms or ducts: |
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Hair hygrometer |
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Psychrometer |
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Diverse electronic hygrometers |
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A hair hygrometer needs adjustment each time it |
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is used if reasonable accuracy is to be maintained. |
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A psychrometer (wet and dry thermometer) does |
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not require adjustment if its thermometers are of |
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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
152 |
DKRCC.PF.000.G1.02 / 520H1459 |
© Danfoss A/S (AC-DSL/MWA), 10 - 2006 |
Fitters notes |
Trouble shooting - Measuring instruments |
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Hygrometer (continued) |
A hair hygrometer can be adjusted by winding |
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a clean, damp cloth around it and then placing |
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it in an airtight container with water at the |
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bottom (no water must be allowed to enter the |
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hygrometer or come into contact with its bulb). |
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The container with hygrometer is then allowed |
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to stand for at least two hours in the same |
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temperature as that at which measurements are |
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to be taken. |
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The hygrometer must now show 100%. If it does |
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not, the setting screw can be adjusted. |
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Ae0_0049 |
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<![if ! IE]> <![endif]>shooting Trouble |
© Danfoss A/S (AC-DSL/MWA), 10 - 2006 |
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153 |
Fitters notes |
Trouble shooting - Fault location (Danfoss commercial refrigeration controls) |
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Contents |
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Page |
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Faults on refrigeration systems, general . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
157 |
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Fault location without . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
. 157 |
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the use of instruments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157 |
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Categorisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157 |
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Knowledge of the system is required . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
. 157 |
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Theoretical knowledge is necessary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
158 |
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Visible faults and the effect on the system operation . . . . . . . . . . . . . . . . . . . . . . |
. 159 |
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Visible faults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
159 |
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Air-cooled condenser . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
159 |
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Water-cooled condenser . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159 |
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Receiver with sight glass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159 |
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Receiver stop valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
159 |
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Liquid line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
. 159 |
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Filter drier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
. 159 |
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Sight glass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
159 |
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Thermostatic expansion valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
. 160 |
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Air cooler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
. 160 |
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Liquid cooler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
160 |
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Suction line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161 |
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Regulators in suction line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
161 |
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Compressor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161 |
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Cold Room . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
161 |
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General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
. 161 |
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Faults that can be felt, heard or smelled and the effect on the system operation . . . . . . . . . . 162 |
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Faults that can be felt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162 |
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Solenoid valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
162 |
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Filter drier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
. 162 |
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Faults that can be heard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162 |
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Regulators in suction line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
162 |
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Compressor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162 |
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Cold room . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
162 |
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Faults that can be smelled . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
. 162 |
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Cold room . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
162 |
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Refrigeration system with air cooler and air-cooled condenser . . . . . . . . . . . . . . . . . . |
163 |
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Refrigeration system with two air coolers and air-cooled condenser . . . . . . . . . . . . . . . |
164 |
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Refrigeration system with liquid cooler and water-cooled condenser . . . . . . . . . . . . . . |
. 165 |
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Guide to fault location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
. 166 |
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System fault location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
167 |
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Fault location on the thermostatic expansion valve . . . . . . . . . . . . . . . . . . . . . . . |
175 |
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Fault location on the solenoid valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
177 |
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Fault location on the pressure control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
. 179 |
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Fault location on the thermostat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
180 |
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Fault location on the water valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
181 |
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Fault location on the filter or sight glass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
182 |
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Fault location on the KV pressure regulator . . . . . . . . . . . . . . . . . . . . . . . . . . . |
<![if ! IE]> <![endif]>shootingTrouble |
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183 |
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© Danfoss A/S (AC-DSL/MWA), 10 - 2006 |
DKRCC.PF.000.G1.02 / 520H1459 |
155 |
Notes
156 |
DKRCC.PF.000.G1.02 / 520H1459 |
© Danfoss A/S (AC-DSL/MWA), 10 - 2006 |
Fitters notes |
Trouble shooting - Fault location (Danfoss commercial refrigeration controls) |
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Faults on refrigeration |
This booklet deals with common faults in small, |
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systems, general |
relatively simple refrigeration systems. |
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The faults, fault causes, remedies and effects on |
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system operation mentioned also apply to more |
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complicated and large systems. |
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However, other faults can occur in such systems. |
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These and faults in electronic regulators are not |
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dealt with here. |
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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 |
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first section deals exclusively with faults that |
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can be observed directly with the senses. Here, |
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symptoms, possible causes and the effect on |
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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 |
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is built up, its function and control, both |
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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).
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Ae0_0029 |
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<![if ! IE]> <![endif]>shooting Trouble |
© Danfoss A/S (AC-DSL/MWA), 10 - 2006 |
DKRCC.PF.000.G1.02 / 520H1459 |
157 |
Fitters notes |
Trouble shooting - Fault location (Danfoss commercial refrigeration controls) |
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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.
Ae0_0033
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) |
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Visible faults and the effect on the system operation Text in [ ] indicates fault cause
Visible faults |
Effect on system operation |
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Air-cooled condenser |
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a) Dirt, e.g. grease or dust, sawdust, dried leaves. |
Faults under a), b), c), d), e) create: |
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[Lack of maintenance] |
- Increased condensing pressure. |
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b) |
Fan stopped. |
- Reduced refrigeration output. |
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- Increased energy consumption. |
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[Motor defect] |
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For an air-cooled condenser, the difference between air inlet |
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[Motor protector cut-out] |
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and condensing temperatures should lie between 10 K and 20 K, |
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c) Fan rotates in wrong direction. |
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preferably at the lower end. |
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[Installation error] |
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d) |
Fan blades damaged. |
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e) |
Fins deformed |
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[Rough treatment] |
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Water-cooled condenser |
For a water-cooled condenser, the difference between condensing |
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with sight glass: See “Receiver”. |
and water inlet temperatures should lie between 10 K and 20 K, |
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preferably at the lower end. |
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Receiver with sight glass |
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Liquid level too low. |
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[Insufficient refrigerant in system] |
Vapour/vapour bubbles in liquid line. |
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[Overcharged evaporator] |
Low suction pressure or compressor cycling. |
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[Overcharged condenser during cold period] |
Low suction pressure or compressor cycling. |
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Liquid level too high. |
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[Overcharged system] |
Excessive condensing pressure possible. |
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Receiver stop valve |
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a) |
Valve closed. |
System stopped via low-pressure control. |
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b) |
Valve partly closed. |
Vapour bubbles in liquid line. |
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Low suction pressure or compressor cycling. |
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Liquid line |
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a) |
Too small |
Faults under a), b) and c) cause: |
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[Sizing error] |
Large pressure drop in liquid line. |
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b) |
Too long |
Vapour in liquid line. |
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[Sizing error] |
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c) Sharp bends and/or deformed |
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[Installation error] |
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Filter drier |
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Dew or frost formation on surface. |
Vapour in liquid line. |
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[Filter partly blocked with dirt on inlet side] |
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Sight glass |
Risk of: |
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a) |
Yellow |
Acid formation, corrosion, motor burn-out, water freezing in |
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[Moisture in system] |
thermostatic expansion valve. |
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b) |
Brown |
Risk of wear in moving parts and blockage in valves and filters. |
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[Dirt particles in system] |
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c) Pure vapour in sight glass. |
Standstill via low-pressure control or compressor cycling. |
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[Insufficient liquid in system] |
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[Valve in liquid line closed] |
Standstill via low-pressure control. |
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[Complete blockage, e.g. of filter drier] |
Standstill via low-pressure control. |
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d) Liquid and vapour bubbles in sight glass. |
All faults under d): |
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[Insufficient liquid in system] |
Compressor cycling or running at low suction pressure. |
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[Valve in liquid line partly closed] |
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[Partial blockage, e.g. of filter drier] |
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[No subcooling] |
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© Danfoss A/S (AC-DSL/MWA), 10 - 2006 |
DKRCC.PF.000.G1.02 / 520H1459 |
159 |
<![if ! IE]> <![endif]>shooting Trouble |
Fitters notes |
Trouble shooting - Fault location (Danfoss commercial refrigeration controls) |
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Visible faults and the effect on the system operation (cont.) |
Text in [ ] indicates fault cause |
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Visible faults |
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Effect on system operation |
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Thermostatic expansion valve |
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a) |
Thermostatic expansion valve heavily frosted, frost on |
Faults under a) cause operation at low suction pressure or |
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evaporator only near valve. |
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compressor cycling via low-pressure control. |
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[Dirt strainer partly blocked] |
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[Bulb charge partly lost] |
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[Previously described faults causing vapour bubbles in |
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liquid line] |
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b) |
Thermostatic expansion valve without external pressure |
Faults under b), c) cause operation at low suction pressure or |
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equalisation, evaporator with liquid distributor. |
compressor cycling via low-pressure control. or compressor |
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[Sizing or installation error] |
cycling via low-pressure control. |
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c) |
Thermostatic expansion valve with external pressure |
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equalisation, equalising tube not mounted. |
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[Installation error] |
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d) |
Bulb not firmly secured. |
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Faults under d), e), f) lead to overcharged evaporator with risk of |
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[Installation error] |
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liquid flow to compressor and compressor damage. |
e)Entire bulb length not in contact with tube. [Installation error]
f)Bulb placed in air current.
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[Installation error] |
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Air cooler |
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a) Evaporator frosted only on inlet side, thermostatic expansion |
Faults under a) cause: |
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valve heavily frosted. |
High superheat at evaporator outlet and operation at mostly low |
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[Thermal valve fault] |
suction pressure. |
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[All previously described faults that cause vapour in |
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liquid line] |
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b) Front blocked with frost. |
Faults under a), b), c), d), e) cause: |
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[Lacking, incorrect or wrongly set up defrost procedure] |
- Operation with mostly low suction pressure. |
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c) Fan does not run. |
- Reduced refrigeration output. |
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- Increased energy consumption. |
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[Motor defect or motor protector cut-out] |
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For thermostatic expansion valve controlled evaporators: |
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d) |
Fan blades defective. |
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The difference between air inlet and evaporating temperatures |
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e) |
Fins deformed. |
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should lie between 6 K and 15 K, preferably at the lower end. |
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[Rough treatment] |
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For level-controlled evaporators: |
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The difference between air inlet and evaporating temperatures |
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should lie between 2 K and 8 K, preferably at the lower end. |
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Liquid cooler |
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a) Thermostatic expansion valve bulb not firmly secured. |
Causes overcharged evaporator with risk of liquid flow to |
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[Installation error] |
compressor and compressor damage. |
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b) Thermostatic expansion valve without external pressure |
Faults b), c) cause: |
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equalising on liquid cooler with high pressure drop, e.g. |
- Operation with mostly low suction pressure. |
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coaxial evaporator. |
- Reduced refrigeration output. |
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[Sizing or installation error] |
- Increased energy consumption. |
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c) Thermostatic expansion valve with external pressure |
For thermostatic expansion valve controlled evaporators: |
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equalisation, equalising tube not mounted. |
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The difference between air inlet and evaporating temperatures |
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[Installation error] |
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should lie between 6 K and 15 K, preferably at the lower end. |
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For level-controlled evaporators: |
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The difference between air inlet and evaporating temperatures |
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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 effect on the system operation (cont.) Text in [ ] indicates fault cause
Visible faults |
Effect on system operation |
|
Suction line |
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a) |
Abnormally severe frosting. |
Risk of liquid flow to compressor and compressor damage. |
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[Thermal valve superheat too low] |
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b) Sharp bends and/or deformation. |
Low suction pressure or compressor cycling. |
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[Installation error] |
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Regulators in suction line |
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Dew/frost after regulator, no dew/frost ahead of regulator. |
Risk of liquid flow to compressor and compressor damage. |
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[Thermal valve superheat too low] |
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Compressor |
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a) Dew or frost on compressor inlet side. |
Liquid flow to compressor with risk of compressor damage. |
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[Superheat at evaporator outlet too low] |
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b) Oil level too low in crankcase. |
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[Insufficient oil in system] |
System stop via oil differential pressure control (if fitted). |
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[Oil collection in evaporator] |
Causes wear of moving parts. |
c) Oil level too high in crankcase. |
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[Oil overfilling] |
Liquid hammer in cylinders, risk of compressor damage: |
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[Refrigerant mixed with oil in too cold a compressor] |
- Damage to working valves. |
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[Refrigerant mixed with oil because superheat too low |
- Damage to other moving parts. |
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- Mechanical overload. |
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at evaporator outlet] |
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d) Oil boils in crankcase during start. |
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[Refrigerant mixed with oil in too cold a compressor] |
Liquid hammer, damage as under c) |
e) Oil boils in crankcase during operation. |
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[Refrigerant mixed with oil because superheat too low |
Liquid hammer, damage as under c) |
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at evaporator outlet] |
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Cold Room |
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a) Dry surface on meat, limp vegetables. |
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[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. |
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c) Defective or missing alarm sign. |
Can give rise to personal injury. |
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d) Defective or missing exit sign. |
Can give rise to personal injury. |
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For b), c), d): |
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[Lack of maintenance or sizing error] |
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e) |
No alarm system. |
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[Sizing error] |
Can give rise to personal injury. |
General |
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a) Oil drops under joints and/or oil spots on floor. |
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[Possible leakage at joints] |
Oil and refrigerant leakage. |
b) |
Blown fuses. |
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[Overload on system or short-circuiting] |
System stopped. |
c) Motor protector cut-out. |
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[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 |
161 |
<![if ! IE]> <![endif]>shooting Trouble |
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. |
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[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 |
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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 |
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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 |
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Defective alarm system. |
|
[Lack of maintenance] |
Can give rise to personal injury. |
Faults that can be smelled |
Effect on system operation |
Cold room |
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Bad smell in meat cold room. |
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[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 |