Maintenance Service and Trouble Shooting
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
20
