Crankcase Heaters

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belly band crankcase heater

When I first started in the trade as an apprentice we worked on a lot of Trane heat pumps that used crankcase heaters that slid into the compressor sump on the big orange Tyler reciprocating compressors like the one below.

It was very common for these heaters to break off where the wire entered the rod and short against the bottom of the condensing unit. Some of the old timers I worked with would say “This is Florida, we don’t need those things here”, disconnect it and move on.

I later learned that isn’t the correct approach

Systems that have crankcase heaters, have them for a reason and while outdoor ambient temperature is one factor it isn’t the REASON crankcase heaters exist. Refrigerant is attracted to the refrigerant oil in the compressor when the system goes into the off cycle, the amount of refrigerant in the oil and the rate at which it moves into the oil depends on the type of refrigerant and oil and the temperature of the compressor.

When the compressor is off for a while a significant quantity of refrigerant can migrate to the compressor and condense. When the compressor comes on the refrigerant rapidly expands and foams the oil, forcing it out of the compressor and into the system. This is called a “flooded start” and will eventually result in compressor damage due to lack of lubrication, it also decreases system efficiency due to the oil in the system inhibiting the transfer of heat.

Strategies like hard shut off expansion valves, liquid line solenoids help to keep liquid refrigerant out of the compressor and oil separators help to keep the oil in the compressor and out of the systems but the trusty old crankcase heater is still a simple and commonly used strategy to prevent flooded start. If you find one that is failed you would be better off replacing it instead of taking the word of techs who tell you just to cut it out, like I once did.

— Bryan

 

 

 

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One comment

  1. Reza hakim says:

    love the class
    its been awhile since i last worded on crankcase heaters ,but none the less nice class

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