AC Unit Not Operating


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Old 05-09-14, 09:39 AM
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AC Unit Not Operating

Hi, I have a Trane XE100 central air unit. Toward the end of the season last year the circuit breaker for the compressor (dual pole 60) started tripping, but since it was the end of the year I let it go (yeah I know bad move).

Called the local service company I've used for years. he came out and said the fuses were blown and that the compressor was shot. $7K new unit was the recommended solution (this was after I explained that I've been unemployed and don't have $7K). So I started thinking and wondered if the fuses were shot, how could he tell the compressor was bad? So I bought two fuses and replaced the ones that were blown. I turned the thermostat down and the inside fan came on as well as the fan in the outside unit, but not the compressor. So I bought a new contactor and capacitor, switched the old ones out, but now the inside fan will run, but not the outside fan. I took videos of the connections to the contactor and capacitor so I'm 99% certain I connected the wires correctly.

I'm stumped why the outside fan isn't running (and I wish the compressor was too). Can anyone give me some guidance what I may be doing wrong, or if there is something else I should be looking at from this point.
 
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Old 05-09-14, 09:47 AM
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Sorry, it's a Trane XE1000 unit...
 
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Old 05-09-14, 10:33 AM
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Where are the fuses that were bad, as you mentioned that the circuit breaker was tripping last year. Are the fuses in the disconnect box outside? When the thermostat is calling for cooling, is the contactor pulled in? Do you have a voltmeter? If you do, have you checked to see if you have 240VAC on both sides of the contactor when the thermostat is calling for cooling?

See this thread: http://www.doityourself.com/forum/ai...tor-input.html. See the image of a contactor that PJmax posted. It shows you where you should measure voltages on the contactor, and what to expect.
 
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Old 05-09-14, 11:27 AM
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I replaced the fuses that were outside in the disconnect box.

I do have a multi meter but it's been a long time since I've used it. Trying to find a good refresher online.

Since I posted this I tried pushing in the contactor with a pencil. That got the fan to run, but I'm not sure if the compressor kicked in when I did that. I was glad to see the fan run but don't know why the contactor isn't closing on its own
 
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Old 05-09-14, 11:38 AM
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Since the condensor fan (outside fan) originally came in after replacing the fuses (before you replaced the contactor and capacitor), either the contactor is defective or it's wired incorrectly (most likely a wiring error).

Set your multimeter on a sufficiently high AC volts scale and use it to measure some of the voltages that PJmax referenced in his diagram (other thread). If you don't have 24VAC coming into the outside unit, it's possible that you blew the low voltage fuse. Many systems use a small fuse (typically 3 amp) in series with the 24VAC transformer to prevent the transformer from burning out should the output of it get shorted. It's possible that you inadvertently shorted the 24VAC line and blew the fuse. The only way to properly check all this out is by taking voltage measurements at various points in the system.
 
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Old 05-09-14, 11:46 AM
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OK figured out the multimeter. With the thermostat calling for cooling, I get 242 volts at L1 L2, and 26 volts at the sides. Noting coming out (because the contactor isn't closing.

I just replaced the contactor today so it should work unless its defective.
 
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Old 05-09-14, 01:35 PM
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It appears that it's wired correctly, as you have the expected voltages (except for the output). It sounds like the contactor is defective. Do you still have the old one? If so, try replacing the new contactor with the old one and see if the fan comes on. If it does, then it would appear that the new contactor is defective.

Once the condenser fan runs, then you can proceed to determine why the compressor isn't running. One thing you can check (with the power turned off) is that the wiring to the compressor is good. Sometimes there is a poor connection resulting in the wire getting hot and breaking off. Follow the heavy wires from the outuput of the contactor to the compressor, checking for burned or broken wires or poor connections (particularly any "push on" terminals).
 
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Old 05-09-14, 01:51 PM
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With the inside unit hot & the tstat calling for cool , and the outside disconnect off , all you should have inside the condenser / outdoor unit is your 26 VAC . This should pull in your contactor , whether it be the old one or new one .

Measure voltage at the contactor coil ? 26 VAC ? You may or may not have some limits / safeties in series with the 26 VAC coil circuit ? Like high or low pressure switches ? Maybe even overloads ?

You may have to find the wiring diagram and trace that down ?

When you get the contactor pulling in , when the tstat is calling for cool , you are ready for the next step . Come back for the next step in trouble shooting the condenser .

God bless
Wyr
 
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Old 05-10-14, 10:07 AM
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Hi everybody, thanks for the advice. I called in a contractor who said its the overload switch in the compressor. I did have some additional questions about how to proceed from here they are in this thread:

http://www.doityourself.com/forum/ai...ompressor.html
 
 

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