Quick service tip: Handling hermetic compressor burnouts

May 12, 2000
A common cause of compressor failures that we must contend with is the burnout of the motor in hermetically sealed compressors. This failure is generally the result of a reduction in the dielectric integrity (resistance) of the motor winding insulation.

In air conditioning systems, when excessively high temperatures occur in the refrigerant system, the thermal stability point of the refrigerant may be reached. When this happens, the refrigerant may break down.

As HCFC-22 has chlorine and fluorine in its chemical makeup, hydrochloric and hydrofluoric acids may be produced. These acids are corrosive and will damage the compressor motor winding insulation.

The resulting reduction in insulation resistance will create an increase of electron flow (amperage) through the conductive refrigerant surrounding the motor to ground. Due to this loss of amperage to ground, the amperage requirement of the motor is increased.

The more severe the contamination, the greater the increase in amperage draw. When the amperage draw exceeds the rated load amps of the motor, heat builds up in the motor windings, causing the eventual burnout of the motor.

Cleaning up the right way

The correct handling of system cleanup and compressor replacement after a burnout is of the utmost importance.

Before the prohibition on venting of chlorinated halocarbons, R-11 was commonly used to flush systems after burnouts. This was very effective because R-11 is a good solvent.

Since the prohibition, other system flushing products have been introduced. Great care must be exercised when using these products because they can become trapped in the system and may be difficult to remove.

The best method to protect the replacement compressor and ensure against additional failures is to install an oversized liquid line filter-drier and a properly sized suction line filter-drier.

Filter-drier desiccants clean the refrigerant and oil of acids that may remain in the system. The oil can be tested after some run time of the replacement compressor to verify that no acids are present. Also, a megohmmeter can be used to test the dielectric strength of the winding insulation to verify that it is free of contamination.

The suction line filter-drier should be removed after cleanup is complete and replaced with a suction filter with a bypass feature. If this is not done, the filter-drier may become restricted, causing excessive suction line pressure drop.

This pressure drop has a direct impact on compressor performance, causing an increase in compression ratio, power consumption, and a reduction in system capacity.

Using these simple procedures should prevent additional compressor failures and result in a satisfied customer.