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Old 04-29-2010, 11:00 PM   #1
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A/C unit keeps throwing circuit breaker


Good Evening. First time user, so please bare with me. Today, for no apparent reason, one of two a/c units failed to cool (unit for the upstairs br's, ground floor unit fine). My wife noticed after a while that the circuit breaker had tripped. she searched on line for troubleshooting, and did a couple of the steps, and I replaced the circuit breaker with same type, thinking it had gone bad. When I hooked it back up, breaker stayed on for a few seconds, we heard what sounded like a growl, then the breaker tripped. tried one more time and same this happened. Trying to figure out what is wrong. Repair techs in this town charge arm and leg and will tell you lie to eek out extra money when not necessary. Any help will be greatly appreciated, even if for no other reason than I can challenge a tech as to what the problem is, versus what he may be trying to pull over on us. Thanks in advance. Additional info... home built in 2006, so still fairly new. no wire appear loose nor corroded in the box....

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Old 04-29-2010, 11:23 PM   #2
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A/C unit keeps throwing circuit breaker


What you are describing is likely the compresor locked up.
definently not DIY. Need an ammeter to diagnose.

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Old 04-29-2010, 11:27 PM   #3
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A/C unit keeps throwing circuit breaker


Also check that you are getting 240v +/- 10% or +/-5% measured at the AC unit. The nameplate will say what minimum voltage it needs.

Last edited by Yoyizit; 04-29-2010 at 11:30 PM.
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Old 04-30-2010, 08:20 AM   #4
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A/C unit keeps throwing circuit breaker


Since you heard a humming/growling sound.

Good chance either the compressor or condenser fan motor is shorting out.

Don't reset the breaker again, until the problem is found and repaired. Continued resetting of the breaker will cause more harm to your system if its a short in the compressor.

Acid clean up can become very expensive. And continued resetting of the breaker, can cause more and more acid to form in the system.
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Old 04-30-2010, 06:04 PM   #5
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A/C unit keeps throwing circuit breaker


You can do a little testing. Turn the breaker off first. Disconnect the wires going to the compressor,write down what went where as you pull each wire off. Try the system again. If the fan runs then it's the compressor. If the breaker trips then disconnet the fan leads and try again. Look for wires shorted to ground outside in the AC. Mice love to make them home for the winter and will chew on wire insulation,yellow and red must taste the best.
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Old 04-30-2010, 08:25 PM   #6
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A/C unit keeps throwing circuit breaker


Quote:
Originally Posted by Marty S. View Post
You can do a little testing. Turn the breaker off first. Disconnect the wires going to the compressor,write down what went where as you pull each wire off. Try the system again. If the fan runs then it's the compressor. If the breaker trips then disconnet the fan leads and try again. Look for wires shorted to ground outside in the AC. Mice love to make them home for the winter and will chew on wire insulation,yellow and red must taste the best.
Good idea.
This test is free & simple to do and no instruments are necessary so why not do it? The OP might luck out.

Last edited by Yoyizit; 04-30-2010 at 08:27 PM.
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Old 04-30-2010, 08:41 PM   #7
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A/C unit keeps throwing circuit breaker


I worked with a guy that did that test. After he removed the wires from the compressor. The breaker didn't trip. So he condemned the compressor. I went with him to help get the compressor on the roof.

After we were up and had the recovery machine running. He told me how he determined the compressor was bad.

I went and got my meter up and checked the windings. No shorts to be found anywhere.

Started checking the rest of the system. Found the short in the condenser fan motor. it wasn't enough to trip the breaker unless the compressor was also running.


Just a FYI.

And we didn't change out the compressor. Instead, the company ended up with a 5 ton compressor instock.
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Old 04-30-2010, 08:45 PM   #8
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A/C unit keeps throwing circuit breaker


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Originally Posted by beenthere View Post
it wasn't enough to trip the breaker unless the compressor was also running.
That was a long shot. . .

With the money that's riding on a correct diagnosis, sounds like the OP may need a clamp-on ammeter and the motor current specs.
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Old 04-30-2010, 09:03 PM   #9
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A/C unit keeps throwing circuit breaker


Vast majority of condemned compressors. Aren't bad compressors.


Test meters, and procedures can help minimize that number.
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Old 05-01-2010, 11:44 AM   #10
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A/C unit keeps throwing circuit breaker


Quote:
Originally Posted by beenthere View Post
Vast majority of condemned compressors. Aren't bad compressors.


Test meters, and procedures can help minimize that number.
For a resi compressor, what ohm readings probably mean
1. good?

How 'bout for
2. bad?

For #1 I'd guess between and 1 and 5 ohms
#2, less than 1 ohm or more than 5 ohms.

Same question for the fan.

Last edited by Yoyizit; 05-01-2010 at 11:48 AM.
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Old 05-01-2010, 11:50 AM   #11
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A/C unit keeps throwing circuit breaker


Its not so much what the ohm reading is as a single number(should not have a reading to ground though).
But if the start to common and run to common add up to the start to run amount.

1 ohm isn't a bad reading. for a start to common reading.

Amount of reading also varies by winding temp.
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Old 05-01-2010, 05:25 PM   #12
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A/C unit keeps throwing circuit breaker


How's these look?

..........Run....... Start.............. Run........ Start
Model Winding... Winding.... Model Winding. Winding
022 1.42 - 1.64 2.14 - 2.46 026 1.22 - 1.41 1.30 - 1.50
030 1.14 - 1.32 1.37 - 1.57 038 0.83 - 0.95 1.20 - 1.38
036 0.91 - 1.05 1.66 - 1.90 049 0.59 - 0.68 1.41 - 1.63
042 0.81 - 0.93 1.36 - 1.57 064 0.46 - 0.52 0.56 - 0.64
048 0.51 - 0.59 1.13 - 1.30 072 0.34 - 0.40 0.50 - 0.57
060 0.42 - 0.48 0.74 - 0.85
070 0.34 - 0.40 0.51 - 0.59


I'm gonna' have to measure mine while the thing still works. . .
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Old 05-01-2010, 06:42 PM   #13
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A/C unit keeps throwing circuit breaker


Motors are induction loads.

While any of the above readings could be ok. They could also be high or low, depending on the temp of the windings at the time.
And weather its a recip or scroll compressor.

Compressor winding readings are taken to check if they are open, and then also added together to check for shorting and or shunting.

The start to run equaling the start to common and run to common are more important then the individual readings.
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Old 05-01-2010, 08:05 PM   #14
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A/C unit keeps throwing circuit breaker


Must frustrate the "scientists" out there who figure everything is black and white. No substitute for real world experience.
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Old 05-01-2010, 09:32 PM   #15
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A/C unit keeps throwing circuit breaker


Life would be so much easier if everything was black and white.

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