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Question DetailsAsked on 8/20/2014

If my compressor capacitor cap dies, should I also replace the compressor motor?

The system is a 2007 variable speed unit. The tech says that this is a sign that the motor is on its way down hill.

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3 Answers

Voted Best Answer

A failed capacitor can effect the compressor, but not often,I wouldn't consider changing the compressor if it is operating just fine, we change hundreds of capacitors per year and compressor changes are rare.

I don't agree that a failed capacitor is a sign that the motor/compressor is on it's way down.


Answered 4 years ago by BayAreaAC


A "compressor capacitor cap" - that is the protective sheet metal cover over the capacitor - about a $5 item. I am assuming you mean the starting capacitor for the compressor motor. While a poorly lubricated compressor, hence causing hard starting, can wear out a capacitor and cause its failure, I would not say that its failure is generally an indication of compressor problems - they just give up the ghost after enough starts.

Starter capacitor is usually about $10-40, though I have seen them up to $100 for the pricier brands - also on the higher side ($30+) if a dual capacitor that provides starting for both the compressor and the fan. Install should be minimum service charge - say $75-125 range - only takes 2 to 15 minutes to replace depending on brand. An easy DIY thing if if at all electrically inclined - usually just shut off power, cover plate or cap removal, loosen the clamp or strap that holds it, pull off a few press-on wire clips (keeping track of which go where), slip out, put new one in, hook up wires, tighten clamp, replace cover and you are ready to turn back on. Just VERY important to get right replacement part.

I certainly would not be looking at replacing the motor unless it starts taking out capacitors frequently - most motors (as long as they are not covered in debris and dirt or flooded) will run decades - much longer than the compressor will last, as a rule.

Answered 4 years ago by LCD


The tech's written estimate/ explanation is more specific - it was a bad cap on the OD fan motor and that the motor is pulling higher than usual amps (note: the heat index today was 106) and the motor should be replaced as well. His verbal comments to me included reference to the capacitor. Does this change anything?

Answered 4 years ago by Guest_9674809


Unfortunately, not all motors are rated at the same ambient temperature, and current draw does not vary linearly with ambient temperature, but rather depends a lot on the cooling of the motor. 106 heat index is about 1/3 above design (test) temperature and probably, for an AC fan, at the NEMA operating temperature design limit, which is normally 40C, or 104C.

SAFETY NOTE on following - test first with a very quick tap with wet finger before placing any part of hand against it for more then a fraction of a second, same way you would check if a pot or panor toeaster or portable barbecue ewas too hot to move - assume it may be well above boiling hot if motor is severely overheating.

If the motor is not running noticeably hot on the outer casing and end bearing areas (have someone turn it off at the breaker, NOT THE THERMOSTAT, immediately before you touch it) - it will normally be what you would probably call luke-warm, perhaps "hot" but not uncomfortably so. If too hot to hold your hand on for an extended period, then is running overly hot, and if very hot at the end bearings (typically blunt center disc of back of case, and where shaft comes out of front of casing) then that is an indication it should be lubricated if can be (some are sealed bearings), and if sizzling hot definitely toasted or well on its way, so to speak.

If the motor is overheating, either due to bearing wear or due to localized overheating in the internal windings, that would make it harder starting, which would wear out the capacitor faster. Still, unless "hot" by the above test, I would just replace the capacitor and cross my fingers. If it starts going out slowly, typically it will start hard, commonly dimming the lights for several seconds during the start cycle. Of course, if unit starts stalling - trying to start but failing and clicking off after maybe 5-10 seconds, then shut off power to it and call technician. Ditto if it starts failing to cool, because a failed cooling fan will make the entire system run hot and possibly not even cool at all, and of course can damage the other components in the system as well if left to run without the fan for a period of time.

Answered 4 years ago by LCD

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