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-   -   HVAC Will not turn on (http://www.diychatroom.com/f17/hvac-will-not-turn-72683/)

grasshopah 06-02-2010 09:37 PM

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

Marty S. 06-02-2010 10:59 PM

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.

grasshopah 06-03-2010 09:15 PM

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

mikethe ductman 06-03-2010 11:06 PM

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.

beenthere 06-04-2010 05:48 AM

Quote:

Originally Posted by mikethe ductman (Post 450903)
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.

mikethe ductman 06-04-2010 06:49 AM

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


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