Stop Misdiagnosing Compressors: Why Your Continuity Test is Failing You

Many HVAC technicians are unknowingly misdiagnosing dead compressors by relying on the continuity setting on their multimeters. While continuity is excellent for checking circuits that should be connected (like fuses or a closed light switch), it's completely inadequate for accurately testing for a grounded compressor. Continuity mode provides an audible "beep" when resistance is extremely low, but it has a very limited range for detecting higher, yet still problematic, resistance values. This means you could get no beep and assume a compressor is good, when in reality, it's faulty.

The proper way to test for a grounded compressor is by using the resistance (ohms) setting on your multimeter. Unlike continuity, resistance mode measures a wide spectrum of ohms, from zero all the way up to millions. Manufacturers like Copeland and Danfoss specify that any resistance reading below 1 million ohms (1 Megaohm) from a winding to the compressor's casing indicates a failed, grounded compressor. So, if your continuity test gives no beep, switch to ohms, and you might find a reading of, say, 1,700 ohms – a value far below 1 Megaohm, clearly indicating a grounded and failed compressor that the continuity test completely missed. Always remember, continuity is for connections, resistance is for everything that shouldn't be connected.