Refrigerant migrates to the coldest part of the refrigeration system during off cycle. A crankcase heater is an accessory that keeps the compressor warm, thus preventing liquid refrigerant from migrating to the compressor.
There are two basic types of heaters: insertion and external. Each has advantages and the manufacturer has made the decision on which to use on each unit based on the type of unit and intended use.
When liquid refrigerant is present in the compressor in small amounts it mixes with the oil and provides poor lubrication for the crank-shaft and main bearings. If large quantities of refrigerant are present in a compressor, refrigerant will mix with some oil and also stratify or form layers.
When the unit starts you can get liquid refrigerant pumped through the bearings and you will get a foaming action as the refrigerant starts to boil out of the oil. The foam does not do a good job of lubricating. This condition will cause excessive wear and bearing failure.
By doing autopsies on compressors, I have found that many failures originally thought to be electrical were mechanical failures that caused the compressor to lock up and the motor winding to fail.
Because crankcase heaters use electrical energy I have been asked to turn them off in cold weather because the client isn't using the air conditioner. But the client runs the risk of not turning the heater on next heating season.
Also, by keeping the compressor warm, the electrical connections imbedded in the compressor will not sweat, causing corrosion and high resistance connections causing failure. The cost of operation is low – similar to a 100-watt light bulb.
If a client's unit does not have crankcase heaters, install a universal band type. If he does have crankcase heaters, check them for proper operation.
Tech Tip by Frank Prah, CMS, CLS Facilities Management Services
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