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Discussion Forum

AC unit keeps on burning up start capacitors

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TimMiller

09-11-2009 00:26:32
98.198.130.39



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Our a/c unit keeps on burning out starter capacitors. Its now on its second. I just put it in a few months ago. Did the start relay or something possibly go out? I have though about installing a totally new start kit for it. Any suggestions would be great. I'd like to save 50 bucks on a start kit if I can, but 50 bucks is a whole lot cheaper than a new compressor.




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TimMiller

09-13-2009 00:20:14
70.243.40.67



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 Re: AC unit keeps on burning up start capacitors in reply to TimMiller, 09-11-2009 00:26:32  
I will do that. Another thing i just thought of is i will check for voltage drop across the disconnect switch. I know it sounds weird but the disconnect on our other unit went bad, and since they were both installed at the same time, it could have been a bad run. I will let you know when i get back home and start doing some probing.



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TimMiller

09-12-2009 01:53:02
70.241.31.146



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 Re: AC unit keeps on burning up start capacitors in reply to TimMiller, 09-11-2009 00:26:32  
The a/c unit already had a start kit installed. I will replace the potential relay along with the start and run caps. (isnt the potential relay the relay that comes with the start kit) I replaced the contactor when i installed a new capacitor the last time because it was getting quite burned looking.



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T_Bone

09-12-2009 10:22:54
64.57.205.153



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 Re: AC unit keeps on burning up start capacitors in reply to TimMiller, 09-12-2009 01:53:02  
Hi Tim,

Yes, MOST start kits come with a new potential relay and start cap as were trying to change the OEM compressor phase angle design to compensate for a out of specification compressor winding.

Since the unit already has a start kit installed, I would install a new potential relay and start cap to the OEM compressor specifications and see what happens. A start lit may not be required or help.

To get a better idea of what your dealing with, use a accurate DVOM too measure the windings (all three) then compare to the OEM spec's and see where you stand. Also preform a winding too ground test using a analog meter. You could be wasting your money on a new kit if the compressor is too far gone.

More likely than not, you could find the compressor wired wrong. Besure to identify the CSR of the compressor terminals and trace the wiring circuit back too each cap.

Even if you preform the above testing, upon start up while taking voltage and amperage measurements, you could discover that the compressor is shot, either/both electrical or mechanical.

If you have extensive electrical knowledge, you can make a very cheap compressor testing set up using a momentary switch.

T_Bone

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Whizkidkyus

09-11-2009 19:13:04
64.130.131.20



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 Re: AC unit keeps on burning up start capacitors in reply to TimMiller, 09-11-2009 00:26:32  
Sounds like something could be putting too much or too little power / amps to the capacitor and overworking it and possibly overheating it or something on that order.

Whizkidkyus



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Whizkidkyus

09-11-2009 19:01:42
64.130.131.20



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 Re: AC unit keeps on burning up start capacitors in reply to TimMiller, 09-11-2009 00:26:32  
Sounds like something could be putting too much or too little power / amps to the capacitor and overworking it and possibly overheating it or something on that order.

Whizkidkyus



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TimMiller

09-11-2009 11:38:02
98.198.130.39



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 Re: AC unit keeps on burning up start capacitors in reply to TimMiller, 09-11-2009 00:26:32  
When i mean start capacitor going bad, the guts of the cap is leaking out. I have a capacitor tester also, not very cheap but very well worth the money.



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T_Bone

09-11-2009 15:41:33
64.57.205.153



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 Re: AC unit keeps on burning up start capacitors in reply to TimMiller, 09-11-2009 11:38:02  
Hi Tim,

Your POTENTIAL relay is bad. Always replace both capacitors when replacing the potential relay. NOT replacing the caps CAN cause a compressor failure and I could care less what your cap-meter shows as there wrong 75% of the time.

Potential relays are compressor specific so be sure to copy the info on the relay as well as the COMPRESSOR tag I.D. Buy the wrong relay and you'll burn up the compressor.


Your wasting your money buying a hard start kit as when that happens, your compressor is just about shot. 90% of the time, it won't help.

T_Bone

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tech4

09-11-2009 11:23:46
72.15.91.136



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 Re: AC unit keeps on burning up start capacitors in reply to TimMiller, 09-11-2009 00:26:32  
In my case the voltage start relay had welded contacts that kept the start capacitor in at all times. I opened the relay and burnished the contacts and been working ok since. I could not find the correct start relay since it is an obsolete unit but still works fine.



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GUIDO

09-11-2009 07:41:09
71.168.244.25



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 Re: AC unit keeps on burning up start capacitors in reply to TimMiller, 09-11-2009 00:26:32  
Hello TimMiller,
Sounds like a low voltage problem to me.
I would check for bad connection, try the contactor input point first, then the compressor side connection of the contactor. While the unit is starting check the voltage at the contactor output. It will just take one bad leg/connection to make the capacitor go bad in a few starts. Next you can check the terminals at the compressor connections, look for discolored ends. If all check O.K. You may have a tight compressor, and a starting kit should take care of that.
Good Luck............Guido.

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buickanddeere

09-11-2009 06:29:54
216.183.154.214



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 Re: AC unit keeps on burning up start capacitors in reply to TimMiller, 09-11-2009 00:26:32  
Low voltage due to small wires and long runs can be a factor.
I've seen replacement start capacitors with insufficient voltage ratings.We used to blow the paper start capacitors to bits on the feed mill until they were up-rated.



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greygoat

09-11-2009 06:13:57
98.125.73.9



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 Re: AC unit keeps on burning up start capacitors in reply to TimMiller, 09-11-2009 00:26:32  
I recently purchased a CAPACITER TESTER, it
wasn"t cheap, but sure is nice for checking
magnetos, older tractors, and electric motors.
I wish that i"d had one years ago.



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MarkB_MI

09-11-2009 02:52:52
166.203.98.20



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 Re: AC unit keeps on burning up start capacitors in reply to TimMiller, 09-11-2009 00:26:32  
What is your definition of "burning out"? Can you see physical damage to the capacitor? Did you test it with an ohmeter?

Testing a capacitor with a multimeter is easy: Disconnect at least one lead of the capacitor. Put the meter on the "ohms" scale, and connect the meter leads to the capacitor. The resistance reading should initially be a dead short (zero ohms), then it will quickly rise to infinity (overrange). Reverse the meter leads and you'll briefly see a NEGATIVE resistance, then it will rise again to infinity.

If you don't see this behavior, the capacitor is either open or shorted. Otherwise the capacitor is fine and you need to look elsewhere.

Note that capacitors have a very wide tolerance and can change value over time. So it's possible that changing the capacitor would cause the motor to briefly work, even if the capacitor was not the root cause of your problem.

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36 coupe

09-11-2009 16:24:43
216.220.251.121



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 Re: AC unit keeps on burning up start capacitors in reply to MarkB_MI, 09-11-2009 02:52:52  
Testing capacitors with a 1 1/2 volt battery used in an ohmmeter is a waste of time.



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MarkB_MI

09-12-2009 04:51:52
166.203.74.56



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 Re: AC unit keeps on burning up start capacitors in reply to 36 coupe, 09-11-2009 16:24:43  
OK, Coupe, what do you use to test capacitors?

Most folks only have a multimeter to work with. Personally, I've never seen a failed capacitor that passed the simple multimeter check.



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36 coupe

09-17-2009 15:11:45
216.220.250.181



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 Re: AC unit keeps on burning up start capacitors in reply to MarkB_MI, 09-12-2009 04:51:52  
Start capacitors can lose value.My tool box has a mid range start capacitor with leads and clips on it.Too low in capacity make motors start very slow,too high and the motor starts too fast.I have 3 RC testers in the shop, one for each bench.Start capacitors are best checked by substitution.Your ohmmeter battery can not detect leakage ,a big problem in small capacitors.I started in electronics in 1950.

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T_Bone

09-13-2009 09:52:34
64.57.205.153



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 Re: AC unit keeps on burning up start capacitors in reply to MarkB_MI, 09-12-2009 04:51:52  
Hi Mark,

I too have always used a AVOM for testing run/start caps with using the flip lead method. I found that this was just as accurate as using a good cap tester. Although DVOM's can be used, I found AVOM's best for my usage.

On run/start caps, were more concerned that the capacitor is functioning than with the actual capacitance of the cap. Run/start caps are of large capacitance to begin with, so a small deviation lack of capacitance was not a critical loss like it would be in a electronics circuit where we deal with small capacitance values that greatly effect the circuit performance.

I was just thinking about all the thousands of caps that I've tested in 45yrs, I can only remember replacing a dozen or so in compressor circuit designs.

A few capacitors tested good but the compressor circuit failed too run/start, but when replaced with a "new" capacitor of the same value, the compressor circuit would once again function as designed. Although rare, this does occur.

T_Bone

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36 coupe

09-17-2009 14:58:02
216.220.250.181



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 Re: AC unit keeps on burning up start capacitors in reply to T_Bone, 09-13-2009 09:52:34  
Capacitors do lose value.



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da-bees

09-11-2009 00:53:21
76.187.61.125



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 Re: AC unit keeps on burning up start capacitors in reply to TimMiller, 09-11-2009 00:26:32  
If the unit was put in a few months ago,the compressor is normaly warrantied 5 years.Using a hard start kit will often cure the problem. An inductive amp meter will tell you if it is staying on start windings to long. I'm thinking it will be difficult for form to do more than guess at the problem. If you have access to and know how to use meters,someone here can walk you thru a couple of tests that will tell them enough to help you much better. Good luck

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