We get calls in the branch fairly regularly from customers that have a compressor that has open windings – so they think. In talking with them for a short time we will find out that the compressor body is warm or sometimes even hot. Many times, the compressor is just off on either the internal or external overload. I know from talking to Copeland and Tecumseh, that this is a very common misdiagnosis.

A technician that has not run across this before goes back to his training and checks resistance of the windings. The diagnosis seems simple – no resistance between two of the legs and the compressor must be bad? The reality is that almost every compressor manufacturer has some type of overload on their compressor that can lead to a misdiagnosis. The compressor does not necessarily have to be hot but just warm to the touch.

The overload can trip for many reasons but more than likely, it will be a high amperage and/or a high compressor temperature situation. This can be caused by faulty electrical components, mis-wiring, defective contactor or breaker, wrong rotation (3 phase scrolls only), low refrigerant charge, no cooling back to the compressor, dirty condenser etc.

The first step is to cool the compressor down. Due to the mass of steel and copper, these overloads can take as long as two hours to reset! We usually tell the customer to shut the power off, put a bag of ice over the compressor and go to lunch. By placing ice on the compressor, this will drastically reduce the stand-by time and will reset the overload very quickly. Sometimes while you are there, you can actually hear the overload reset with a distinct “ting”. Once the overload has reset, you should now be able to check your windings. If the windings now show OK, power up the compressor – but, be careful! Something caused the compressor to go off on the overload to begin with, so make sure you have all your diagnostic devices hooked up on start up (amp meter, volt meter, manifold gauges, temperature probe etc.).

Once you get the overload to reset and the compressor will run, it is normally very easy to determine what caused the overload trip to begin with. Correct the problem and you just saved a lot of time and money for a compressor change. And remember the overload is there to save the compressor from these system problems – never jump one out!

**This article would apply to all welded and scroll compressors and 2 & 3 cylinder semi-hermetic compressors. The 4, 6, & 8 cylinder semi-hermetic compressors use a solid state overload that is a little more complicated to troubleshoot.**