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The compressor's discharge temperature is often an overlooked temperature when troubleshooting a refrigeration or air conditioning system. However, it is very important because it's an indication of the amount of heat absorbed in the evaporator and suction line, and any heat of compression generated by the compression process.
Because the compressor's discharge temperature is superheated, a pressure-temperature relationship does not exist and it must be read directly on the discharge line by some sort of temperature-measuring device.
The compressor's discharge temperature should be measured about 1 to 2 inches away from the compressor on the discharge line. This discharge temperature should never exceed 225°F. Carbonization and oil breakdown can occur if compressor discharge temperatures exceed 225°.
The three causes for high discharge temperatures are:
* High condensing temperature.
* Low evaporator pressures and temperatures.
* High compression ratios.
HIGH CONDENSING TEMPERATURE
There are many potential causes of high compressor discharge temperatures. A high condensing temperature is one of them.
When the condensing temperature is high, the compressor must compress the refrigerant from the low-side (evaporating) pressure to an elevated high-side (condensing) pressure. This added work done by the compressor would raise the heat of compression. Thus, the compressor's discharge temperature will be higher.
Remember, condensing temperature is the temperature the refrigerant is as it changes from a vapor to a liquid in the condenser. There is a pressure-temperature relationship with the condensing temperature because of the phase change. A gauge reading on the high side of the system is all that is needed to find the condensing temperature. Convert this pressure to a temperature using a pressure-temperature chart. This is the condensing temperature.
However, there are many causes for high condensing temperatures,...