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Any electrical engineers out there?

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I think my air compressor needs a new capacitor.  Turn it on and it hums and tries to start but just can't get it done.  Especially if it is cold out.  The compressor is a cheap Briggs and Stratton unit and part are not available any longer.  I need to find a suitable substitute and am like a monkey with an abacus looking at all the options.  Ohms, volts, micro feraunds, I can't find a match.  Some are close but others are way off.  Anyone want to help out an electrically challenged cowboy?

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I have had good luck finding start/run capacitors at hvac supply houses, the ones contractors use. They have a dizzying array of capacitors. Look up and see if there is a Ferguson, United Refrigeration, or Johnstone Supply nearby. I go to United Refrigeration, since it’s just 1 mile from my favorite electric supplier ( I’m a licensed electrical contractor) If it has legible print, they should be able to test it and get you one, if they don’t already have it.  My particular Fluke multi meter actually has a capacitance test feature ( most don’t). Most HVAC guys I know have a dedicated capacitance tester and it may be worth the service call charge to an independent contractor, to see if he’s willing to come out, test and locate a new capacitor, if needed. The capacitor may be fine. You may find out it’s a motor failure. Some motors have start run capacitors with start run relays. I have seen relays fail to switch from start to run, though I have to admit I don’t fool with many compressors with capacitors; mainly 3 phase industrial compressors . 
 

My observation has been HVAC guys buy and replace more motor capacitors, and replace more single phase motors, than anyone in service trades, therefore are generally better at working on small single phase motors than nearly anyone out there.

 

Edited by Dirty Dan Dawkins

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47 minutes ago, Wallaby Jack, SASS #44062 said:

how close is close ?

Well the voltage might be the same but then that micro feraund (u with a funny f) thing will be much lower.  I just don't know enough about one or the other to make sense of it. I may have to take it to work and let my maintenance guys look at it .  Thanks for your help.

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41 minutes ago, Dirty Dan Dawkins said:

I have had good luck finding start/run capacitors at hvac supply houses, the ones contractors use. They have a dizzying array of capacitors. Look up and see if there is a Ferguson, United Refrigeration, or Johnstone Supply nearby. I go to United Refrigeration, since it’s just 1 mile from my favorite electric supplier ( I’m a licensed electrical contractor) If it has legible print, they should be able to test it and get you one, if they don’t already have it.  My particular Fluke multi meter actually has a capacitance test feature ( most don’t). Most HVAC guys I know have a dedicated capacitance tester and it may be worth the service call charge to an independent contractor, to see if he’s willing to come out, test and locate a new capacitor, if needed. The capacitor may be fine. You may find out it’s a motor failure. Some motors have start run capacitors with start run relays. I have seen relays fail to switch from start to run, though I have to admit I don’t fool with many compressors with capacitors; mainly 3 phase industrial compressors . 
 

My observation has been HVAC guys buy and replace more motor capacitors, and replace more single phase motors, than anyone in service trades, therefore are generally better at working on small single phase motors than nearly anyone out there.

 

 

I did a search and a lot of hvac stuff came up. I'll check with our service techs. Thanks.

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When it does start, check the running amps when it is getting close to high pressure shut off. Hook your amp probe on the load side of the breaker, assuming it's a 115 volt unit. I just change out the motor, motors are relatively cheap if you have a good source. 

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What info is on the motor data plate?

 

what is the uF number on the capacitor?

 

 The replacement capacitor needs  have the same uF rating as the old one give or take 10%. 


 Voltage rating needs to be the same or greater than the old one. 

BTW

110, 115, and 120 voltage ratings are all interchangeable. 
 

208, 220, and 240 voltage ratings are all interchangeable. 
 

 

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As far as voltage goes you can use any voltage capacitor from 110 to 480 volts as long as  it's equal  or greater than yours. When testing a capacitor for uf's if it test bad it's bad if it test good it could be bad. There cheap enough just replace it. What's the uf reading on your capacitor?

I can help you out if  you can't locate one. 

Hells Comin 

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14 hours ago, Sedalia Dave said:

What info is on the motor data plate?

 

what is the uF number on the capacitor?

 

 The replacement capacitor needs  have the same uF rating as the old one give or take 10%. 


 Voltage rating needs to be the same or greater than the old one. 

BTW

110, 115, and 120 voltage ratings are all interchangeable. 
 

208, 220, and 240 voltage ratings are all interchangeable. 
 

 

 

3 hours ago, Hells Comin said:

As far as voltage goes you can use any voltage capacitor from 110 to 480 volts as long as  it's equal  or greater than yours. When testing a capacitor for uf's if it test bad it's bad if it test good it could be bad. There cheap enough just replace it. What's the uf reading on your capacitor?

I can help you out if  you can't locate one. 

Hells Comin 

 

 

It says 140 uf +/- 5%.  250 V.  AC 50/60 Hz.  25/70/21   C   P1

It has a model number of CBB65.  I don't have the motor information at the moment.  I'll have to get it.

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Why not just remove it and take it to a parts place along with info on compressor...I tend to remember that a  capacitor were sold by size, working volts and wattage...

 

Texas Lizard

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