A/C System no longer working properly

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Old 04-04-10, 09:46 PM
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A/C System no longer working properly

My central air conditioner system is no longer functioning properly. 2 months ago it ran fine when I tested it. Now, I've got the following symptoms:

When I turn the tstat to COOL, and the fan to AUTO the outside compressor kicks on and continues to run. No unusual sounds from the compressor. Inside, the air handler kicks on and runs for 30 - 35 seconds and then shuts off. About 5 minutes later, it kicks on again, runs for 30 - 35 seconds, and then shuts off. All during this time, the compressor remains running. The air handler, when running, pulls air from the single whole house return (filter removed for cleaning) but the volume of air being ejected from the supply vents is not impressive (but I don't know if the velocity of the air has changed or not. I can't remember what it was like before).

I thought maybe the blower motor was bad, ruined, or no longer functioning at 100%, since power surges and outages are frequent here, or that maybe the coils in the air handler were icing, and that was why the blower fan stopped working after 30 seconds. But now I'm not so sure.

I turned everything off, then let it sit for 1 hour. Then I set the tstat to OFF but turned the fan from AUTO to ON. The result is a humming sound from the air handler for 1 minute, but no air movement, and then the humming sound stops. But if I then switch the tstat from OFF to COOL, there is air movement again for 30 seconds before it shuts off.

I thought maybe the tstat was bad, so I swapped it with one from a functioning system on another zone, but that made no difference. Symptoms described above were identical.

My system was constructed in 1999, and it is near the sea, so corrosion on outside components is a given, and as I mentioned previously, power surges and outages are common, so voltage damage is possible. But everything was working fine 2 months ago when tested.

Thanks for any ideas on trouble shooting. I'm on one of the out islands in the Bahamas, and would rather have some idea of what is happening before I call for service. I've got a volt/ohm meter but no pressure gauges to check freon levels.

Thanks!
 
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Old 04-05-10, 02:37 PM
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seems like the motor is going off on thermal overload and u need a new one. the auto and on on the tstat usually activate different speeds of the motor and thats why one speed doesnt work at all and one works for 30 seconds, before getting too hot
 
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Old 04-06-10, 11:13 AM
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Thanks for the reply. Can you think of any way that I can test that hypothesis before I buy a replacement motor? Can I disconnect the motor from the air handler, wire it directly, and see what happens? I've got a Trane system. I thought it might also be possible that there is some kind of circuit board on the air handler in the attic that has been fried by a power surge, and maybe that was a problem?
 
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Old 04-06-10, 01:04 PM
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Originally Posted by DrR137 View Post
Thanks for the reply. Can you think of any way that I can test that hypothesis before I buy a replacement motor? Can I disconnect the motor from the air handler, wire it directly, and see what happens? I've got a Trane system. I thought it might also be possible that there is some kind of circuit board on the air handler in the attic that has been fried by a power surge, and maybe that was a problem?
Clamp on amp meter should do it.
 
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Old 04-12-10, 06:02 AM
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I agree, sounds like its going into thermal overload. Did you open the fan section of your air handler and check to be sure that the fan spins freely? There should be no binding and it should spin easily. Many of those motors have oiling ports, maybe it needs serviced? That humming sound sounds like the motor is binding, especially with the report of no airflow when it hums.

Before you cleaned your filter was it badly clogged? These motors are what is known as air-over. The motor is cooled by the air that is moving over it. Maybe your filter was so clogged that no air moved, you may have toasted it and this is the result. If you experience power problems as you describe, you may also have browned out. When you experience a brown out situation you wil notice dim lights, this indicates a low voltage situation and it will fry a motor.
 
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