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with pressure gauges. If the gas suction valve block is broken, the suction pressure gauge pointer
will swing violently and the suction pressure will be very high. Whereas when the gas discharge
valve block is broken, the discharge pressure gauge pointer will swing drastically and the
discharge pressure will be very high. In both cases, stop the compressor at once. If possible, open
the cylinder cover, check the valve block, and repair it.
•
Compressor suddenly stops
Very often, when the compressor suddenly stops, the gas suction pressure and/or discharge
pressure have exceeded their respective prescribed ranges. When this happens, the pressure-
operated protective relay automatically shuts off the power to the compressor. Below we discuss
the reasons for high gas discharge pressure and low suction pressure.
Stoppage due to excessively high gas discharge pressure
1) High gas discharge pressure due to excess refrigerant
Analysis of Trouble
Loose frosting and poor refrigerating effect may occur if excessive refrigerant has been charged
into
the system. Excess refrigerant will occupy additional space in the evaporator.
This will reduce its heat dissipating area, and the phenomenon of “liquid striking” may occur.
Condensation may occur on the gas return tube, and the gas discharge pressure will 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 charge the system with a proper quantity of refrigerant.
2) Air in the system
Analysis of Trouble
The residual air in the system will circulate with the refrigerant in the system. The major
symptoms are higher gas discharge pressure, higher discharged gas temperature, and poor
refrigerating effect. The gas discharge pressure will exceed its maximum value when the
compressor has run for an extended period, and activates the protective relay.
Remedy
Check the air has been in the refrigerating system. Generally, there are three possibilities. First,
is that the air has been sucked into the system during repairs due to carelessness. Secondly, it has
not been completely purged evacuating the system. The third possibility is that there are leak
points at the low-pressure end of the refrigerating system. Leak points appear in low temperature
parts or assemblies. This is because the evaporation temperature is lower for such low
temperature devices, especially at the low-pressure end; it is easier for the air to go into the
