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Old 06-02-2010, 08:37 PM   #1
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HVAC Will not turn on


Hi

I have a 10+ yr AC that will not turn on.
The thermostat clicks but then nothing. The unit i has a Honeywell ST9120 G4004 fan controller.

I disconnected the thermostat and on the fan controller when I connect the

R+Y = cooling starts
R+W = Heat starts
R+G = Fan starts

I do not know whether the Thermostat or the Fan controller is broke. Ideas/thoughts anyone?

Thanks

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Old 06-02-2010, 09:59 PM   #2
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HVAC Will not turn on


Your tests confirm the funace,blower and AC work without the thermostat so the problem is the thermostat or a thermostat wire. Hook the controler back up then twist the wires at the stat to see which it is.


Last edited by Marty S.; 06-02-2010 at 10:01 PM.
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Old 06-03-2010, 08:15 PM   #3
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HVAC Will not turn on


Thanks for the reply.

It turned out that there was drip pan switch connected in series. For some reason the switch was "open" even though the pan was bone dry.

Removed the drip pan switch from the circuit and the AC blows coool!

Have to look around for a drip pan switch now
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Old 06-03-2010, 10:06 PM   #4
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HVAC Will not turn on


HUH?
If that is the case when you jumped r-y nothing should have happend.
Oh well maybe the cooling you were talking about was just the blower coming on.
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Old 06-04-2010, 04:48 AM   #5
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HVAC Will not turn on


Quote:
Originally Posted by mikethe ductman View Post
HUH?
If that is the case when you jumped r-y nothing should have happend.
Oh well maybe the cooling you were talking about was just the blower coming on.
If he jumped R to Y directly at the control board in the furnace/air handler. that would bypass the wet switch. If the wet switch is wired to the R or Y from stat to board.
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Old 06-04-2010, 05:49 AM   #6
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HVAC Will not turn on


Oh ok I thought he took the t-stat off and jumped r-y

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