Heat Pumps and Electric Heating - capacitor rating
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dbrucem2
10-25-09, 07:58 AM
I replaced the fan and cap on my heat pump this summer, with a little help from this forum. :)
The other day, I found the fan running in reverse (only once). I've been monitoring it, and it hasn't run in reverse since that one time last week. Now, however, I have to sometimes kickstart the fan to make it run.
My first assumption is bad run cap. So my question is regarding the capacitor ratings. I know it's a 7.5 microfarad/370V, however since its a dual cap, what is the first larger number for? i.e. 55+7.5mfd,370V How concerned with this first number should I be when replacing?
My assumption, again, is that this first number is for the compressor motor.
The other day, I found the fan running in reverse (only once). I've been monitoring it, and it hasn't run in reverse since that one time last week. Now, however, I have to sometimes kickstart the fan to make it run.
My first assumption is bad run cap. So my question is regarding the capacitor ratings. I know it's a 7.5 microfarad/370V, however since its a dual cap, what is the first larger number for? i.e. 55+7.5mfd,370V How concerned with this first number should I be when replacing?
My assumption, again, is that this first number is for the compressor motor.
Houston204
10-25-09, 11:22 AM
You are correct, the larger value is for the compressor.
(Dual Cap)
http://i151.photobucket.com/albums/s160/Houston204/MotorWiring.jpg
The cap can be measured with certain meters..
http://i151.photobucket.com/albums/s160/Houston204/Searsmeter.jpg
Capacitors can hold a charge for a few minutes after removing power, be careful. You'd measure Herm to Com and Fan to Com.
Color codes vary.
(Dual Cap)
http://i151.photobucket.com/albums/s160/Houston204/MotorWiring.jpg
The cap can be measured with certain meters..
http://i151.photobucket.com/albums/s160/Houston204/Searsmeter.jpg
Capacitors can hold a charge for a few minutes after removing power, be careful. You'd measure Herm to Com and Fan to Com.
Color codes vary.
dbrucem2
10-25-09, 04:24 PM
Awesome info. We have a Fluke DMM on the bench at work, so I might borrow it one evening this week.
I was surprised when looking on the schematics on the unit. The fan is 7.5mfd 370V and the compressor is 35mfd 440V. Is it common to see both voltage ratings on the same unit? I'm not arguing w/ the manufacturer, I just figured they would be consistent.
I was surprised when looking on the schematics on the unit. The fan is 7.5mfd 370V and the compressor is 35mfd 440V. Is it common to see both voltage ratings on the same unit? I'm not arguing w/ the manufacturer, I just figured they would be consistent.
Houston204
10-25-09, 05:24 PM
Most meters do not measure capacitors. It would display Cap, Ufd or Mfd. I have seen a Fluke 29 that could measure caps.
I use Fieldpiece...
http://i151.photobucket.com/albums/s160/Houston204/Fieldpiece.jpg
I use Fieldpiece...
http://i151.photobucket.com/albums/s160/Houston204/Fieldpiece.jpg
Former Member
10-26-09, 05:18 PM
Several Flukes have the microfarad check capacity I use a Fluke 16
Houston204
10-27-09, 07:14 PM
It looks like Fluke uses the circuit symbol.
http://i151.photobucket.com/albums/s160/Houston204/Fluke16.jpg
http://i151.photobucket.com/albums/s160/Houston204/Fluke16.jpg