Fan Motor on AC Unit will not turn off


The Fan on my AC unit will not turn off even if I turn everything off on the thermaostat, only thing that will turn it off is flipping the breaker. I have changed the contactor and thermostat out and it hasn't fixed the problem. What else could the problem be?
------------------------------------- Jeff Gibson
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On Sat, 11 Sep 2010 21:24:32 +0000, jefflee1975 wrote:

Does the compressor shut off? Is there a separate relay for the fan motor?
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responding to http://www.homeownershub.com/maintenance/Fan-Motor-on-AC-Unit-will-not-turn-off-501276-.htm jefflee1975 wrote:
Hugh Jassolle wrote:

The compressor does shut off, just the fan motor keeps going. thanks
------------------------------------- Jeff Gibson
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On Sat, 11 Sep 2010 21:24:32 +0000, jeffgibson1975_at_yahoo_dot snipped-for-privacy@foo.com (jefflee1975) wrote:

Stuck relay maybe. Sometimes they're on the motherboard. I had a similar problem and had a pro come over. He fixed it in ten seconds by flexing the motherboard, something I would never do. I had tapped around though with a screwdriver handle. We both knew it could stick again, so I had him put in a new motherboard. Think the whole shot was 3-400 bucks. But it also cleared up other goof-ups the furnace had from day 1. Multiple ignition cycles, varying shut down fan cycles, etc. Anyway, might be time to bring a pro in. Changing ignitors is about the limit of my "expertise." The newer stuff - mine is 12 years old and I include that - has a lot of electronics.
--Vic
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jefflee1975 wrote the following:

My AC fan does not turn off when I turn the thermostat off.. Well, at least for 10 - 15 seconds or so. I think it has to go through a shutdown process.
--

Bill
In Hamptonburgh, NY
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You think just maybe he waited more than 15 secs before posting the problem?
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snipped-for-privacy@optonline.net wrote the following:

Never assume anything in a message.
--

Bill
In Hamptonburgh, NY
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On Sep 11, 5:24pm, jeffgibson1975_at_yahoo_dot snipped-for-privacy@foo.com (jefflee1975) wrote:

It seems unlikely that it could stay on if the contactor is releasing. Seems rather impossible as the entire unit gets powered via the contactor. Are you certain the compressor is shutting off and the fan is still running? Use your vom to see where power is coming from. You need to stop replacing parts and start troubleshooting.
I did have a somewhat similar probem because of a short in the double cap. But in that case it was a heat pump and the fan was not shutting off when the defrost cycle started. So there was still power through the contactor but the ground relay on the defrost board couldn't turn off the fan because of the short in the cap.
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I'm thinking that it's the fan limit switch in the furnace. It's easy enough to test or replace. Just take the cover off of it and move it around and see if it's stuck. When they get old they don't move as good as they used to. You should be able to find one cheaper off of eBay, but if you need it right away go to Grainger. The only hard part when I did mine was that they didn't make the exact model number for my old one but I was able to figure out which new one to replace it with. The key is to get one the right length.
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