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Old 08-21-2012, 09:33 AM   #1
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Different Capscitor for replacement motor


Ok, I've been out of the DIY arena for a while so I need some help.

I've replaced the condenser fan motor on a residential HVAC unit and the new motor uses a 7.5 F run capacitor just like this one:

The replacement motor only has three wires: (AS DID THE ORIGINAL)

Black - I assume goes to the power on the circuit board (like the old one)

Brown -
Orange -

The old setup used a start/run capacitor rated at 40/5F (the three terminal cylinder type) which powered both the fan and compressor motors. I know I can't just use this for the new motor as it is rated for 7.5F.

So, here are the questions:

1. Do I just add the new 7.5f run capacitor? And how should it be wired up?

OR...

2. Do I buy a new start/run capacitor (three terminal cylinder type) rated at 40/7.5F? Will the higher F rating damage the compressor motor? ...since the original is 5F

Please advise.....it's hot.


Also, sorry for the misspelled title.....Capascitor?


Last edited by JEOliva; 08-21-2012 at 11:02 AM.
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Old 08-21-2012, 10:23 AM   #2
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Different Capscitor for replacement motor


You can wire brown to one side of the 7.5 cap and orange to the other side of the 7.5 cap and wire black to the contactor, then wire the orange side of the new cap to the opposite side of the contactor as shown in the 3 wire example and leave the old dual cap serving the compressor OR buy a 7.5 / 40 dual cap.



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Old 08-21-2012, 10:35 AM   #3
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Different Capscitor for replacement motor


First of all thank you for the reply.

I don't want to over complicate things but....

the original three wire config., which is similar to your "DUAL CAP" illustration had the BLK going to a circuit board and not directly to the contactor. Is this irrelevant since the BLK ultimately ends up at the contactor T1 even if there is a circuit board in between?

So, the new setup would be like your 3 WIRE diagram. The only wire I would have to add would be a RED wire from T2 to the new run capacitor, thereby eliminating the the DUAL CAP from the fan motor circuit......

Did I get that right?

Also, putting in a higher rated F DUAL CAP will or won't harm the motors rated for lower F?

Again, thanks for the help.
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Old 08-21-2012, 11:07 AM   #4
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Different Capscitor for replacement motor


You need to use the proper cap for the motor, you can go plus or minus 5% of the rating but thats it, otherwise you will damage the motor
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Old 08-21-2012, 11:14 AM   #5
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Different Capscitor for replacement motor


Ok, so I should wire the new RUN CAPACITOR as in the 3 WIRE illustration?
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Old 08-21-2012, 11:17 AM   #6
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Different Capscitor for replacement motor


i would purchase a new dual run cap rated at 40/7.5 and wire it exactly like it was wired before. nothing should need to change, all you are doing is swapping out an existing dual run with a new dual run.
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Old 08-21-2012, 12:00 PM   #7
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Different Capscitor for replacement motor


Thank you all for taking time to respond.

When I read further about Capacitor sizing I did find warnings about improper sizing.

If the capacitor has a lower F rating the motor will not start/run and if it has a higher F rating then evil magnetic forces will be unleashed that can cause the fabric of space-time to unravel and ultimately destroy the universe.....or it makes the motor fail prematurely.....one of those two.

So, I went back to Grainger and got the original run capacitor back along with a handy diagram that is similar to the 3 WIRE diagram that Houston204 provided.

Thank you all again.
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Old 08-21-2012, 12:09 PM   #8
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Different Capscitor for replacement motor


best of luck
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Old 08-21-2012, 12:22 PM   #9
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Different Capscitor for replacement motor


thank god

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