Central Air Conditioner problem

I have a central air conditioner system. I have recently noticed that when I turn off the air conditioning setting on my thermostat (ie. Fan=Auto, System=Off), the air conditioning unit (ie. fan) outside of my house is still running. No air is being pushed thru the vents, however, I can hear air leaking from the unit in the basement, which is connected to the outside air conditioning unit.
To stop the outside fan from running, I had to turn off the power supply to the air conditioning unit.
Does anyone have any suggestion on why the fan would still be running, when the thermostat air conditioning setting is turned off.
Thanks NQ
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snipped-for-privacy@gmail.com wrote:

One obvious possibility is a stuck motor contactor on the compressor unit. But it could also be a flaw somewhere else in the control system.
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Thanks for your reply.
Yes, the air conditioner was working for the last 2 years.
CJT wrote:

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snipped-for-privacy@gmail.com wrote:

If you have a multimeter, and the contactor is accessible, you might check the AC voltage across its coil. If it's zero, but the compressor is still running, then you've isolated your problem -- stuck contactor.
If the coil voltage is 20V +/-, then you need to look upstream (e.g. thermostat, low-voltage wiring, etc.).

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snipped-for-privacy@gmail.com wrote:

Just wondering if the outside fan running is to cool down the condenser. Does it eventually quit? Does the compressor stop when you switch the thermostat?
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The fan stays on and the compresser doesn't stop when I switch the thermostat to off.
Rich256 wrote:

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snipped-for-privacy@gmail.com wrote:

Naturally the compressor should stop.
I don't understand what you mean when you say you hear air leaking. I guess you mean at the evaporator in a furnace.
How about when you set the thermostat to a lower temperature? That should also result in the compressor stopping.
I don't think I have any answers. Only more questions. Does turning the power back on start the compressor again?
I can't think of any reason that the thermostat might cause the problem. My guess might be that a relay is stuck on in the compressor unit.
If so, it might be that just giving it a hit with the handle of a screwdriver would knock it loose.
Unless someone else comes up with something I expect you will have to get someone knowledgeable with the unit to open it up.
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On 13 Jul 2006 17:23:10 -0700, snipped-for-privacy@gmail.com wrote:

Open the thermostat. Disconnect the red wire, if it stops then replace the thermostat, if it doesn't then go outside, open that up, and replace the contactor.
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Thanks for the info.
I suspect the thermostat is the problem, since the airconditioning unit now seems to shut off properly and I am noticing that sometimes the AC unit does not start even when the thermostat is turned on.
Al Moran wrote:

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On my system wich is part of my furnace i have a " on/off manual blower " switch wich is constently hit by accident by the kids, the first time it happened i also thought i had a problem. Check for such a manual blower switch.
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indep wrote:

His problem isn't the blower continuing to run, it's the outside compressor.

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