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Old 05-07-2009, 09:22 PM
 
274 posts, read 559,564 times
Reputation: 305
Default Central A/C Fan Keeps Running

We keep our A/C blower fan in the auto setting. That way it cycles on and off with the compressor. Starting today, the fan keeps running no matter what. I jiggled the on/auto switch... no help.

No problems with the compressor. House is staying cool.

Any ideas?
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Old 05-08-2009, 10:26 AM
 
Location: Apple Valley Calif
7,377 posts, read 11,518,282 times
Reputation: 4956
My guess would be that you need a new thermostat. That's the best and cheapest senerio....
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Old 05-08-2009, 11:19 AM
 
Location: Johns Creek, GA
6,650 posts, read 20,764,852 times
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Quote:
Originally Posted by Hoot Owl View Post
House is staying cool.

Any ideas?
Is the house actually reaching the set temp? You could be low on refrigerant? If not, it could be the relay switch @ the compressor. Condenser units are notorious for collecting leaves and other debris and some of it could be effecting the switch and/or the condenser itself- not allowing for enough heat molecule transfer.
Or it could be the T/stat itself, as mentioned before.
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Old 05-08-2009, 02:19 PM
 
Location: St Augustine
605 posts, read 3,161,066 times
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i would try the thermostat first, you can always take it back to home depot if it doesn't work, if still continues i would guess the switch. i had to replace one once but it wasn't too costly.
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Old 05-08-2009, 03:00 PM
 
Location: Somewhere in northern Alabama
11,500 posts, read 26,037,618 times
Reputation: 14018
Contactor switch at the outside unit. If you are comfortable working with electricity, take the cover off the outside control box and whack the clear plastic relay box with the blunt end of a screwdriver a few times to break the corrosion seal between the contact points. If that works, you'll need a replacement one. Get the part number and unplug the old, plug in the new.

If you aren't comfortable with working outside with electricity, please DON'T do this. The circuits are not GFI protected and you can get bit or electrocuted if you don't know what you are doing.
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Old 05-08-2009, 03:16 PM
 
Location: Knoxville
3,294 posts, read 10,427,689 times
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Harry pretty much covered it.
I would try this. Turn the system OFF at the thermostat and see if that does anything. If it does, then fine. If not, then go 2 more steps.......

2nd. Find the circuit breaker for both the inside unit and the outside unit (assuming it's a split system) and turn it/them OFF.
3rd. Wait a few minutes - give it 5 minutes to be safe.

Then turn everything ON again and see if that changed anything. Sometimes, the units have to be totally shut off so they can re-set and get back to working order again.

If doing that does nothing, then it's likely the thermostat, or thermostat wiring, or a control inside the unit.
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Old 05-08-2009, 11:44 PM
 
3,191 posts, read 5,553,563 times
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Hubby asked-
What is the brand and model #s of the indoor and outdoor units? Is it the indoor fan that is running constantly?
( hubby's in the hvac biz, and gives opinions when I poke him LOL)
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Old 05-09-2009, 09:24 PM
 
274 posts, read 559,564 times
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Quote:
Originally Posted by crazyma View Post
Hubby asked-
What is the brand and model #s of the indoor and outdoor units? Is it the indoor fan that is running constantly?
( hubby's in the hvac biz, and gives opinions when I poke him LOL)
It's the inside blower in the closet (attached to the furnace) that's acting up. Not sure which brand it is.

Tell your husband that the fan is now turning on and off with the compressor - like it should be doing. Not sure why, for a day, it ran constantly.

Thanks. Look forward to your reply.
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Old 05-09-2009, 10:14 PM
 
Location: Katy
82 posts, read 342,780 times
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Yeah I was going to ask if it was the inside or outside fan that you were having trouble with. That makes a huge difference. Usually when I encountered this problem in the past, it was due to the fact that either the thermostat was malfunctioning or the thermostat wire had a short somewhere. There are several wires that run to your thermostat and they are housed inside a covering which if damaged anywhere along the way from the blower through the wall to the thermostat, can result in a number of different issues one of which would be causing your fan to never cut off. This would be due to the hot wire coming into contact with the wire that controls the fan. The thermostat can open and close that circuit, but if they are shorted together somewhere, the thermostat is rendered useless. There are a few other possible scenarios, but that was the most common thing I experienced. The fact that it started randomly and then stopped is a bit of a head scratcher though. Some newer models have circuit boards in them that can go crazy too.
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Old 05-09-2009, 10:53 PM
 
3,191 posts, read 5,553,563 times
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Hubby says it might have something to with the limit control on the indoor unit, or like BBALL said, a short in the thermostat wiring. To narrow it down further, he would really need to know if you have gas or electric, plus the model#s & brand....

That being said, he suggested you contact a HVAC co.because it might be something you can not fix yourself.

This unusual fan operation might turn into something more serious, best to have it resolved by a professional before it might get worse.

Hope that helps, sorry he can't do more
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