When my AC first turns on, it will typically trip the circuit breaker shortly after the compressor and fan start up. If I reset the breaker, and turn the AC back on, it will usually run just fine and cool the house to the set temperature. Of course, the problem occurs again when the temperature at the thermostat rises and triggers the AC to start up again. It sometimes takes two or three resets of the breaker to get the AC to start up. My guess is that the compressor is drawing too much current for some reason – but I don’t know why it’s inconsistent, and I don’t know how to go about troubleshooting this. Any tips before I call out the repair man? The unit is getting close to 15 years old so I’m assuming they’re just going to suggest I replace it.

  • Have you taken care of the unit over the past 15 years, or mostly neglected it? – Tester101 May 9 '15 at 0:06
  • I have only owned the property for a year, and it had set empty for three years before that, so it has likely been neglected. – Zach May 10 '15 at 14:15

Before you call a repair person, check the following: Look at the UL label of the outdoor unit. Find the item marked "Minimum Circuit Ampacity." This is the minimum size of circuit breaker required for your unit. Verify that your tripping breaker is at least this big. If it is too small, then you may need to upgrade the electric service to the unit.

It is normal for a compressor to pull more power during initial startup when pressure on the high and low sides have not yet stabilized and the expansion valve is fully open. After the pressures stabilize and the expansion valve closes somewhat, there is typically a smaller load on the compressor than at startup. The most likely cause for your compressor to over amp during startup is that the run capacitor for the compressor is a little weak. A weak capacitor will still start the compressor, but the compressor will draw higher amperage than it is meant to. This is a $15-$25 part. The existing capacitor can be tested with a multimeter that checks capacitance. If the measured value is less than 90% of the labeled value, then the capacitor must be replaced. Make certain the replacement has an equal or greater voltage rating than the original. The capacitance rating must be the same as the original.

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