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comfortless

comfortmaker C9MPD050F12A3 furnace control?

8 posts in this topic

I have a comfortmaker C9MPD050F12A3 and the heat does not work. The a/c, fan and thermostat all work. There is a seperate furnace control and electronic gas valve. The gas valve has the diagnostic light and the limit switches and the exhaust blower hooked to it. The gas valve diagnostic light says all is fine but the is no power to the exhust blower and the pressure switch is open as called for. There are 6 wires from a block at the furnace control to the gas valve. I do not know what reading I should be getting on these lines to tell if it is a faulty furnace contrlol or gas valve. Anybody know how to test for this?

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At the Furnace there should be 24v AC between R and C.

When "heat" is selected, there should be 24v AC between W and C

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The problem is not at the thermostat lines. I believe it is either the furnace control (an electronic board) or the gas valve (an electronic control device) and I wish to know how to test these devices.

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do you have the 24v AC there where it should be at those times ?

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All gas valves use solenoids. Each solenoid is rated diff. But each solenoid have one thing in common. They must have continuity.

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If you have the 24v and there's no Error Codes

then it's sounds like a bad Controller

OR a bad Inducer Blower Motor

Heating (W) Request:

• 24 VAC signal applied to W terminal of FCB.

Inducer motor turns on and the pressure switch(es) close(s).

• Following a 15 second prepurge delay, after the pressure switches closes, the igniter begins a 17 second warm−up.

• The gas valve is energized, the main burners light and flame is sensed.

• The igniter is de−energized after the main burners ignite.

• FCB will delay blower operation for the 30 seconds timed from the opening of the gas valve.

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Thanks I thought it might be a bad controller. There is no power going to the inducer motor.

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