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Question DetailsAsked on 6/17/2016

can I replace AC capacitor from a 40uf/5uf to a 35uf/5uf 440v...

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1 Answer


Probably will start it but maybe not, but why - should be no problem getting right one at HVAC supply distributor, home improvement box store, online, etc - and a 35 micro farad (measure of the energy it stores) starting capacitor will be 15% short of power compared to the 40uf one it is supposed to have - so the motor will start harder and take longer to get up to speed, which causes heating in the wiring inside it and also in very slow start cases overheats the insulation and the bearing lubrication, which wears it out faster and can cause premature failure. Sort of like keeping using a car battery that is weak and dying - might start the car eventually, but you get a lot more wear and tear cranking it over till it starts - especially, as with a car engine, the lubrication is not working right to protect the bearings till it is up to speed, so the longer it takes to start the more internal wear and tear.

Slow starting (when the motor pulls typically 50-200% more power than when up to speed) might also start causing circuit breaker tripping out, or motor thermal protector breaker tripping out.

(the 40/5 or 35/5 designation indicates this is a dual-start capacitor - starts both the compressor motor (the higher number) and the condensor cooling fan (the lower number).

The poor compressor has to work hard enough as it is, with short-interval restarts under high pressure, slaving out in the hot sun and hot humid days for you (and you probably never even let it work on the nice pleasant cool days, only the miserable hot ones), so give the poor thing a break - and possibly save yourself a thousand or more $ from a premature failure.

Answered 4 years ago by LCD

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