Belly band crankcase heater

When I first started in the trade as an apprentice, we worked on many Trane heat pumps that used crankcase heaters. These crankcase heaters slid into the compressor sump on the big orange Tyler reciprocating compressors. They looked like the one in the picture 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.” They'd disconnect it and move on.

I later learned that isn't the correct approach.

Why are crankcase heaters necessary?

Systems with crankcase heaters have them for a reason, and while the outdoor ambient temperature is one factor, it isn't the REASON why crankcase heaters exist. Refrigerant is attracted to the 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 depend on the type of refrigerant, oil type, and compressor temperature.

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 heat transfer.

Strategies like hard shut-off expansion valves and liquid line solenoids help keep liquid refrigerant out of the compressor. Oil separators help keep the oil in the compressor and out of the systems. However, the trusty old crankcase heater is still a simple and commonly used strategy to prevent flooded starts. 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

P.S. – I also wrote an article about crankcase heaters and single-pole contactors. You can read it HERE. I also talked about that topic on my podcast with Kaleb Saleeby, Eric Kaiser, and Joe Shearer. You can listen to that podcast HERE.