PSA: Capacitor tester lied to me on a 4 year old AC unit in Phoenix

I was diagnosing a no-cool call last July and my ESR meter showed a 45 uF run cap as perfectly fine. The thing tested right at 45.5 uF cold. But after running the compressor for maybe 2 minutes, the unit kicked off on thermal overload. I finally swapped the cap anyway just to check and bam, it ran for 3 hours straight. I guess heat was killing the capacitance once it warmed up. Has anyone else had a cap test good cold but fail under load like that?

2 comments

2 Comments

the_harper4d ago

45 uF is a standard motor run cap, not a start cap.

theabennett4d ago

The "standard" part is what gets me. Those 45 uF run caps are common in HVAC but not really "standard" across the board. More like common in a specific range of motors.