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You can test like resistor. If you heat the thermistor to the specified temperature the sensor will open the circuit.
 

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Discussion Starter #5
I did what you suggested and it is working. My unit looked like it had a power surge. The contactor was fried and I changed that, The power to the compressor was melted and I replaced that, I check the ohms on the compress and it checks out good. What elese could it be? If I disconnect the compressor wires and force the contactor on the fan runs, When the compressor wires are connected it trips the circuit breaker. Any suggestions
 

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Check for continuity between the compressor terminals and one of the copper pipes. Sounds like the compressor or one of the compressor wires is shorted to ground.
 

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MAKE ABSOLUTELY SURE that you DO NOT touch any part of the outdoor unit while testing it. If the compressor is shorted to ground and you touch the condensor YOU become the ground and could DIE.

Pay attention to this story JJ.
 

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Discussion Starter #8
You can ohm it, check the amp draw, and make sure you have voltage to it.

Why do you need to check it??? Problems???
I did what you suggested and it is working. My unit looked like it had a power surge. The contactor was fried and I changed that, The power to the compressor was melted and I replaced that, I check the ohms on the compress and it checks out good. What elese could it be? If I disconnect the compressor wires and force the contactor on the fan runs, When the compressor wires are connected it trips the circuit breaker. Any suggestions
 

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MAKE ABSOLUTELY SURE that you DO NOT touch any part of the outdoor unit while testing it. If the compressor is shorted to ground and you touch the condensor YOU become the ground and could DIE.

Pay attention to this story JJ.


Now I see how this test can be dangerous. Thanks yuri for showing me this. :thumbup:
 

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I did what you suggested and it is working. My unit looked like it had a power surge. The contactor was fried and I changed that, The power to the compressor was melted and I replaced that, I check the ohms on the compress and it checks out good. What elese could it be? If I disconnect the compressor wires and force the contactor on the fan runs, When the compressor wires are connected it trips the circuit breaker. Any suggestions
With all power OFF. And all wires removed from the compressor. When you check the compressor for continuity, check across R and C, S and C, and then R and S. R and S ohm value should equal the sum of the other 2 values.

Next, check from each of the compressor terminals to ground(one of the copper lines attached to the compressor is best), if anyone of them has continuity, the compressor is shorted to ground, and needs replaced. If n one of them do. Check that the run cap is not shorted to ground.

Its possible your compressor has a winding to winding short. That type of short can easily weld the contactor's contacts together, and heat it up enough to look like it was struck by lightening.
 

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JJ and Wayne. BE VERY careful with a stalled/shorted compressor it can develop TREMENDOUS heat inside the compressor and literally blow the white "fusite" plug where the C/S/R terminals attach to the compressor out and you could get blasted with high pressure refrigerant/smoke/burning acidic oil/phosgene gas as it burns up. I have seen this several times and I am sure Beenthere has also. It WILL NOT give you any warning it is blowing, (sometimes makes a growling sound but not always) you DO NOT want to be anywhere near that plug or have your face near it.
 

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And when it blows, if the cover isn't on, it can take a flame and the oil will come out like a blow torch was in the compressor. And if you are infront of it, you probably won't survive the burns.
 

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If you are manually pushing in the contactor and before doing this verified you have power to it and it is not starting and blowing the c/b you may have a locked rotor in the compressor (ng).
If you have an ohm meter and clamp it around the feed wire going into the compressor and the amps double the name plate full load amps the compressor is (ng).
Make sure you check the wires at the compressor terminal to see if thay are all tight and have not fallen off the terminals.
When ever you are working on the condenser always wear eye protection and body protection such as gloves etc...

We had a job today with two compressors in one unit. One terminal was completely blown off of both compressor contactors, wires were burnt in several places, when we disconnected the wires from the compressors they checked good no grounds and no shorts. After we replaced the contactors and shorted wires we started both compressors and they both ran good.
 

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If you have voltage going to a crankcase heater you can use an infared thermometer to see if the crankcase heater is operating. Aim the laser beam at the heater and see what the temperature is. Checking amps will be really low if you if you check it that way.
Crankcase heaters should only operate when the compressor is not running. The mfg. May have a relay that energizes when the compressor shuts off to activate the heater. You have to know this when testing the heater
 

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Burnt wiring happens all the time in ACs which vibrate and electric furnaces due to the constant heat/cool thermal expansion contraction on the terminals and vibration. The thing that gets guys killed or their eyes burnt from a welders flash when pushing in a contactor is when it it truly shorted and they don't check for grounding etc or even know that could happen.
 
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