Compressor fault location
The starting device and compressor motor may be a wrong choice. The compressor motor or winding
protector may be defective, and the compressor may be mechanically blocked.
Frequent reasons for reduced refrigeration capacity are coking or copper platings due to moisture or noncondensable
gases in the system.
Blown gaskets or broken valve plates are due to peak pressures being too high and short-time pressure
peaks as a result of liquid hammering in the compressor, which may be due to a high refrigerant charge in
the system or a blocked capillary tube.
The voltage may be too low or the pressure too high for the compressor.
Non equalized pressure causes the motor protector to cut out after each start and will eventually result in
a burnt motor winding.
A defective fan will also affect the compressor load and may cause motor protector cut outs or blown
gaskets. In the case of an unsuccessful start and cold compressor up to 15 minutes may pass until the
winding protector cuts the compressor out. If the winding protector cuts out when the compressor is hot
up to 45 minutes may pass until the protector cuts the compressor in again.
Before starting a systematic fault location it is a good rule to cut off the voltage to the compressor
for 5 minutes. This ensures the PTC starting device, if any, is cooled sufficiently to be able to start the
Should a brief power failure occur within the first minutes of a refrigeration process, a conflict situation
(interlocking) may arise between the protector and the PTC. A compressor with a PTC starting device
cannot start in a system that is not pressure-equalized, and the PTC cannot cool so quickly. In some cases
it will take up to 1 hour until the refrigerator runs normally again.
High and low pressure switches
Cut out of the high pressure switch may be due to a condensing pressure too high, probably caused by lack
of fan cooling.
A cut-out low pressure switch may be due to insufficient refrigerant charge, leakage, evaporator frost
formation or partial blockage of the expansion device.
The cut out may also be due to a mechanical failure, wrong difference setting, wrong cut-out pressure
setting or irregularities in pressure.
For more information about compressor service visit: www.secop.com.