Compressors often burn out by overheating caused by above-normal head pressures. Laboratory tests have proven that presence of air, dirt, and moisture in the sealed system contribute to this condition. Compressors are cooled by bypassing cooled oil mixed with vapor refrigerant returning from the evaporator over the windings.

When the compressor operates while the system is undercharged (or out of charge), insufficient cooling of the compressor motor can cause a compressor burnout. Compressor motors can also overheat and burn out by excessive current flow through the windings caused by low voltage supply or a binding compressor.

If the temperature of the circulating oil (mixed with refrigerant) leaving the compressor discharge valve rises to 350°F (177°C), it will break down and form hydrochloric and hydrofluoric acid, sludge, and varnish. The acid will corrode the insulation on the motor windings and increase the operating temperature of the compressor motor. Shortly after this happens, the motor windings will short-circuit and burn out. A compressor burnout is indicated by oil color changing from clear to black (depending on the severity of burnout) and by a very unpleasant, pungent odor. Oil test kits available from refrigeration supply houses can be used to determine the degree of contamination. The test is simple, and instructions are supplied with the kit.

Because compressors are burnt out more frequently by above-normal temperatures caused by high head pressure, condensers should therefore be checked and cleaned on a regular basis. Condenser fins can be cleaned with a long bristle brush and/or high-pressure gas such as nitrogen, air, or carbon dioxide.

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