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What size capacitor?

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 I need to replace the condensor capacitor, and my question is this.... If the numbers are off the capacitor.. Is there a formula to figure out what sixe capacitor you need? ex. 35/5 .... I do replace these from time to time for others but have always had the writing on it. If I need a dual capacitor for a 2 ton heat pump is there a formula or do I have to call a manufacture to find out if I encounter this!!! Thanks For The Help in advance.....

Look on the nomenclature tag on the fan motor. It gives the mfd capacity rating for the motor. A 35/5 cap means the the compressor requires a 35 mfd cap and the fan uses a 5 mfd cap. Installing the wrong capacitor will cause motor failure. It will overheat and melt the windings in about a day if wrong so it is important to not guess. Usually (but not always) a standard quarter horse motor with 1050 speed takes a five mike capacitor. A third horse motor requires a 7.5 microfarad cap. A half horse motor usually takes a 10 MFD cap. I sold Magnetek, AO Smith, and Packard motors when I was in the biz. If you are unsure about matching a motor you do not always go by horse power rating. You go by amp draw. Horse power rating can be faulty but amp draw rating tell no lies.  :rofl: The primary speed on these condenser motors is usually 1050 rpm but more expensive better built motors speed @ 825 require more exotic capacitors with lower ratings. These motors have special fan blades engineered to move air in a specific way. These motors last longer and are way more expensive and if you plan on using a 1050 motor as a replacement you would be screwing up big time. So it is vitally important to get it right. My 2 cents.

Thanks for the info JW,it will be a great help!!!!

If you buy HVAC capacitors with a 440VAC rating they will replace all 370VAC capacitors.
You can not use a 370VAC capacitor on a system that requires a 440VAC.
Additionally if in a pinch to get a unit up and running you can go up in MFD rating by approximately 10% to get you by.

Here's a little something that's good to know. Finding yourself in a situation such as an after hours call at a restaurant where don't have the correct capacitor. Install in parallel two equivalent mfd caps which add up to desired mfd, with same or higher voltage. Example- 7.5/440 and 5/440 = 12.5/440.   Or place two 25 mfd in series. Example~ 1/c total =1/25 + 1/25 = 2/25 = 1/12.5.  C total = 12.5.  Also plus or minus 10 percent on mfd. This is good to know when your in a bind.


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