BG
Contributor
Posts: 626
Reg: 09-12-07
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05-07-12 04:56 PM - Post#2223540
I have a rental unit with a AC/HEAT window unit in it and its tripping the breaker even when its in the off position. I am out of town and just wondering what could cause this. I was told that it sparks when it is first plugged in and then trips the breaker. This is a fairly large unit, about 8 years old and was about 900-1100 new so if its a reasonable repair I would rather keep i.t
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100% CHEVY
Very Senior Member
Posts: 5438
Age: 60
Loc: Helena,Missippi,U.S.A.
Reg: 12-09-04
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05-07-12 05:20 PM - Post#2223547
In response to BG
I would look for a burned off wire inside the control area,at the compressor terminals and at the capacitor(s).
Same wire could be touching bare metal causing the trip.
Mike. 
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 Vaughn
"11th Year" Gold Supporting Member
Posts: 13559
Loc: Colorado Springs, CO
Reg: 08-08-04
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05-10-12 04:51 PM - Post#2224581
In response to 100% CHEVY
You probably have a wire shorted inside the wall receptacle, unless the AC unit's power cord has been damaged in some way. The way the AC unit is wired doesn't change, so either that power cord is shorted or there is something in the wall that is shorted. There is a short somewhere.
Have you tried plugging it into a completely different circuit with a big extension cord (assuming it can't be moved)?
Capacitor - it would depend on how the capacitor is wired up. Usually in a AC unit, a capacitor of any real size is used to help the motor get started. In that situation, it is wired up into the main power supply - but won't normally cause a problem unless something damaged it. If there is evidence of arcing on it, then yes you would need to replace it.
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BG
Contributor
Posts: 626
Reg: 09-12-07
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05-10-12 06:30 PM - Post#2224612
In response to Vaughn
With the ac unpluged the breaker does not trip, would that not mean that the circuit is ok? I am hoping it is something simple.
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100% CHEVY
Very Senior Member
Posts: 5438
Age: 60
Loc: Helena,Missippi,U.S.A.
Reg: 12-09-04
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05-10-12 07:19 PM - Post#2224638
In response to BG
On most window units wired for 220 volts,the 2 hot legs go into the unit where one is considered common,which means it is not switched and is connected to the main switch,the comressor,the fan and capacitors,etc.
Any of the common connections could be burned off and grounded,causing the circuit to short,tripping the breaker.
Fan motors,compressor motors and capacitors can go to ground internally,causing a short circuit.
Newer units have a circuit breaer/GFCI built in to the cord and plug to protect against this.
I'd suggest you un-plug it,open it up and look for problems.Keeping in mind that the caps need to be dis-charged before you touch them or risk getting a shock!
Mike.
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Vaughn
"11th Year" Gold Supporting Member
Posts: 13559
Loc: Colorado Springs, CO
Reg: 08-08-04
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05-10-12 08:11 PM - Post#2224656
In response to 100% CHEVY
If the circuit doesn't trip with it unplugged - and you can use the wall receptacle to power something else - then the circuit is OK, and you have to fix something inside the AC unit.
FWIW, Capacitors that are part of a AC line power supply do not need to be discharged, because they don't store any voltage on an AC line. Capacitors on a DC power supply WILL build up a charge, but not on AC. AC capacitors are basically a short to AC line voltage - all it does is shift the phase of the AC line voltage not quite 90 degrees, but it does not build up a charge. That is why it is used to start AC motors - because the AC capacitors shift the phase sufficiently on a 110 only line to make the motor "think" that it has two phases - which is the only way to start an induction motor with only a 110v ac line. An induction motor has to be started using two phases, but once up to running speed, it can run on one phase. This is why most 110 volt motors have one or two "humps" on the outside of the motor case - it has starting capacitors underneath those sheetmetal humps.
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BG
Contributor
Posts: 626
Reg: 09-12-07
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05-15-12 04:44 PM - Post#2226277
In response to Vaughn
I got back home today and pulled the window unit out to check into it. How can I check the capacitor to see if its bad? I do have a multi meter. Water must have gotten to the common terminals because they are pretty rusty
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Vaughn
"11th Year" Gold Supporting Member
Posts: 13559
Loc: Colorado Springs, CO
Reg: 08-08-04
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05-24-12 04:43 PM - Post#2229418
In response to BG
If you don't have a capacitance measurement on your multimeter - you probably won't be able to test it.
There is ONE thing you can test - and it is only a pass/fail type of thing. You put it on the ohmmeter setting (a higher setting) then measure the resistance between the two terminals. The resistance will slowly climb if you hold the leads on the two terminals and watch for a while. The resistance will climb on a "good" capacitor, because the capacitor is slowly charging up via the battery used in the ohmmeter readings.
It isn't a very good test, because it doesn't measure the capacitance in any real way - but at least you can get a pass/fail on the capacitor.
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