Compressor and fan not starting


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Old 09-05-13, 10:14 AM
J
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Compressor and fan not starting

Okay as my last thread showed I'm having trouble with my central AC unit. I got the blower motor running but now the compressor and fan aren't starting. When I installed the new blower motor I had to crimp some wires together instead of how they installed in my old motor since the motor was slightly different than my older one, would this cause a problem with the compressor and fan?

When I set the thermostat to COOL all we get is a click and a humming sound. If I set it to HEAT everything seems to start up normally. The blower fan starts and runs fine.

I was looking to see if there was another capacitor for that set of motors but I can't find one anywhere. I suspect that this isn't the problem though otherwise I wouldn't get anything when I turn on the heat.

Any suggestions? It's really disheartening to fix one problem only to have another show up.

This is a Trane XL1100 unit if that helps.
 
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Old 09-05-13, 12:05 PM
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Sorry to hear you are still having problems. Can you post the model number of your unit. XL1100 is a series. Is this a gas/electric packaged system?

You stated that when you set the thermostat to COOL all you get is a click and humming sound.

You stated that when you put it to HEAT everything appears to start up normally.

It could very well be a run capacitor for the fan and compressor.

But there are a few different things that could cause what you are experiencing. Here are the most common (not in any particular order):

1. Defective circuit breaker
2. Loose wiring at high voltage connections
3. Bad fuse block connections
4. Bad or weak run capacitor
5. Bad or weak start capacitor
6. Compressor hard starting
7. Contactor with pitted or burned points
8. Etc.

Start by turning off the power to your unit. Look for obvious burn wires and terminals. Check the run and start capacitors (if you have a start cap) to make sure they are not leaking oil or have "bulged" tops. Check the contactor points condition to make sure they are not burned or excessively pitted.

These are the things that you can do if you are comfortable with getting into the unit. Anything else will probably require a voltmeter to measure what is going on with voltages. If you have access to an voltmeter post back and I am sure someone here will be able to get you go farther.
 

Last edited by firedawgsatx; 09-05-13 at 12:41 PM.
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Old 09-05-13, 12:58 PM
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Didn't get any model numbers but it was a packaged unit. It appears to have been dirty contactors causing the problem. Took a rubber mallet and lightly tapped the back of the sheet metal that was holding them then took a vacuum and cleaned up everything around them. Then it fired right up.

I thought it was one of the run caps because it had clear sticky crap all over it so I took it to the same electric supply shop and they said it tested fine and was likely just sap from all the pine trees. He said it sounded like a control board or contactor problem and told me to call someone. Luckily brute force seems to have won the day since it's currently running and working just fine.

Whoever came up with AC is a god.

Thank you for the tips by the way. I'm sure if someone else runs into a problem it will help them out and I will keep them in mind for any future problems.
 
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Old 09-05-13, 01:40 PM
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Glad to hear you got it up and running. I would suggest you replace the contactor as soon as possible. They aren't that expensive and are easy to replace. I always keep a spare contactor and run capacitor for my units. They tend to fail at the most inopportune time and on the hottest day of the year.
 
 

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