A compressor that is shorted to ground or grounded can be a costly issue for clients and can also be a really big problem. If a technician misdiagnoses in this video, we'll take away all the guesswork and dive into how to diagnose this correctly using isolation diagnosis as well as more about tripping. Breakers First, when you find a tripped breaker, it may be tempting just to reset the breaker and see what happens. But don't do it.

Remember the breaker is tripped for a reason. A circuit breaker is designed to open the circuit during a high current event. This will happen very quickly in the case of a shorted or grounded condition, and will happen more slowly when there is a less extreme overcurrent condition during operation. Every time you reset that breaker, you risk creating a major arc or spark.

If the short is inside the compressor, you're just adding carbon and acid to the refrigerant, further contaminating the system. So the first thing we need to do is a thorough visual inspection of all the high voltage wires, terminals, contactor, capacitor, crank case, heater, the breaker itself, and the disconnect. Check for any signs of abrasion or damage, and check for any loose connections or signs of arcing. If anything looks black and or damaged, that's where you need to start next.

Once That's done and any issues corrected. Inspect the compressor leads and terminals themselves right at the compressor. but remember safety first. Make sure to wear gloves and safety GL glasses, especially because those compressor or fusite terminals may be weakened and can pop out, resulting in terminal venting of the internal refrigerant in a dangerous condition.

Next, take a photo of all the wires or tag them before pulling them off the terminals. This will help avoid any miswiring upon reassembly. Now, measure resistance to ground from each terminal. Usually, you're going to do this from terminal to the suction or discharge line on the compressor.

You can use a mega ohm meter or other quality multimeter. Keep in mind that some compressors are still considered good all the way down to5 megaohms from the terminals to ground. This5 megaohms number comes from Copeland especially for scroll compressors. As the windings are immersed in refrigerant and potentially oil, you may read a high ohm resistance to ground and still have a shorted or grounded compressor because that shorted or grounded condition shows up once high voltage is applied.

Keep in mind that the quality of the reading will depend on the quality of the meter used and the resting state of the motor. When you're convinced that the compressor is shorted to ground or grounded, it's time to isolate the compressor tape and strap up the plug or terminals, ensuring they aren't touching anything. Then reassemble the unit and reset the breaker. If it doesn't trip and everything else like the condenser fan motor runs properly, then you've correctly diagnosed the issue as a shorted or grounded compressor.

If the breaker trips again, it's back to the drawing board. You need to test the other components, but at least now you have a step-by step approach to diagnosing a grounded compressor. Remember: accurate diagnosis, safe time and money for your clients, and performing a visual inspection followed by an OM to ground test followed by an isolation diagnosis before condemning. A compressor is shorted or grounded is a best practice.

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