What size capacitor?

[app1]

Hello,
 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.....

[JWWebster]

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.  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.

[app1]

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

[jumptrout51]

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.

[haroldsappliance]

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.

[JWWebster]

What you would do to MAKE a ?? mfd cap is tape 2 ?? mike caps together and jumper them in effect making it twice as strong. Good tip Harold. When I sold caps I made up a few of these for the custs. Also if you have a ??/370 cap you can sub it with a ??440 cap but you cannot sub out a 440 cap with a 370 cap as Jumpy pointed out. It is also important to note that a 440 cap is way more substantial in physical makep than a standard 370 mike cap. Beefier and tougher. Like me!

[haroldsappliance]