Tag: crankcase heater

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

 

 

 

carrier

We keep 2 pole 40 amp 24v coil contactors on all of our vans. They are versatile, reliable and you can replace most residential A/C contactors with them.

There are a few things to watch for though, especially when you have a crankcase heater. Many brands power the crankcase heater constantly and shut it on and off with a thermostat, often mounted on the discharge line (here’s looking at you Trane).  When you replace a single pole with a two pole contactor in this type you need to make sure you connect BOTH sides of the crankcase circuit across the L1 and L2 line side of the  contactor to ensure the heater can function when the compressor is off.

Even more confusing that that…. Look at the diagram at the top and focus on the top left part of the diagram where the crankcase heater is located…

How does that work do you think?….. I will wait while you think it through…. Don’t cheat… Look at it.

This is a common Carrier Heat Pump crankcase heater configuration.

You notice that one side of the heater is going to L1 line side Terminal 1 and the other side is going to L1 load side terminal 2.

So the crankcase heater ONLY functions when the compressor contactor is OPEN and even then it does so by back feeding through the compressor common and back through the run winding of the compressor to the constant powered L2 side of the contactor.

This means if you replace this contactor wire for wire with a 2 pole contactor the crankcase heater will never work. You must put the compressor run wire (yellow) to the bottom of the contactor (L2 line side) instead of the top like it was if you want the crankcase heater to function in this situation…

All of this to remind you, DON’T BE A PARTS CHANGER! Know what you are replacing, why you are replacing it and what each wire and component actually does.

— Bryan

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