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swing drastically and the discharge pressure is very high. In the both cases,
stop the compressor at once, and if technique is available, open the cylinder
cover and check up the valve block, repair it, or replace it with a new one,
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
Maintenance Service and Trouble Shooting
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