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?

3 comments

3 Comments

the_harper2mo ago

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

theabennett2mo 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.

veraramirez4d ago

Is the whole world like that though? I noticed it with batteries too. Like you go to the store for a D battery and there's eight different kinds but half of them don't work in the thing you have. Same with light bulbs. One minute 40 watts is a standard thing and the next minute everything is LED with weird bases.