Maintenance Service and Trouble Shooting
C. Sudden stop of Compressor during Its Running
The cause of sudden stop of a compressor during its running is mostly that the gas
suction pressure and/or discharge pressure exceed their respective prescribed ranges,
thus making a pressure-operated protective relay shut off the power to the compressor
and stop it. In the following we discuss mainly the reasons for causing excessively high
gas discharge pressure and low suction pressure.
1) Stoppage due to excessively high gas discharge pressure
a) Too much refrigerant charged into the system
Analysis of Trouble
The phenomenon, such as loose frosting and poor refrigerating effect, may occur if
excessive refrigerant has been charged into the system. Superfluous refrigerant will
occupy a certain space of the evaporator, thus reduce its heat dissipating area, and the
phenomenon of "liquid striking" may occur, too. Meanwhile, dew or frost condensation
may occur on the gas return tube, and the gas discharge pressure will obviously rise,
when it reaches the threshold value, the protective relay will actuate and shut off the
power supply to the compressor.
Remedy
Open the tubing, re-evacuate and then charge the system with a proper quantity of
refrigerant.
b) Air left in the system
Analysis of Trouble
The residual air in the system will circulate together with the refrigerant in the system.
The major symptoms caused by this residual air is higher gas discharge pressure,
higher discharged gas temperature (the gas discharge tubing is considerably hot when
you feel it with your hand), and poorer refrigerating effect. Furthermore, the gas
discharge pressure will exceed its normal value when the compressor has run for a
period not too long, thus making the protective relay actuate and bring to a stoppage.
Remedy
Check up how the air has been left in the refrigerating system. Generally, there are two
possibilities: one is that the air has been sucked into the system when repairing due to
carelessness, or it has not been purged out totally when evacuating the system; the
other is that there are leak points at the low pressure end of the refrigerating system.
Leak points appear mostly in those low temperature parts or assemblies, because the
evaporation temperature is lower for such low temperature devices, especially at the
low pressure end, it is easier for the air goes into the system. Once it has been
ascertained that air does exist in the system, you have to open the tubing, re-evacuate
it and then charge it with refrigerant.
2) Stoppage due to electric troubles
a) Thermostat is out of control
Analysis of Trouble
In case the thermostat does not work in its good order or its temperature sensor has
not been installed properly, frequent stoppage is also likely to occur.
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