Coleman lp gas furnace won't start


Old 11-06-11, 07:32 AM
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Coleman lp gas furnace won't start

I have a Coleman LP Gas furnace model DGAT070BDF that will not ignite. I am trying to start it for the first time this year. It has a flashing code that says the combustion air switch stuck closed. Any ideas? Also, am trying to find a source where I can download a free service manual as I have just recently moved into this mobile home.
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Old 11-06-11, 11:24 AM
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The pressure switch typically has one or two small rubber hoses going to it and is usually flat and round.

When the thermostat calls for heat the circuit board tests the switch to check that it is open. Then the inducer motor is turned on and the switch should close to verify that the venting system is working properly.

The diagnostic code is suggesting that the switch is stuck in the open position.

I'd use an AC voltemeter to check to see if that's the case when the thermostat is calling for heat.
Old 11-06-11, 04:32 PM
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If this is the furnace I think it is, there is a small damper inside the combustion air duct on the right side of the furnace. This damper is powered by a small 24 volt motor & must open before the furnace will fire. It is common for that damper to stick over the off season.
There is/was a recall on that furnace. Here is the recall notice.
Safety/Inspection Notice
Old 10-18-13, 06:00 PM
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I too have this Coleman furnace model DGAT070BDF in a manufactured home. Tried to start the furnace up for heat, and it would not. Trouble code flashed 4 times(limit switch open) and proceeded to look for the switches. Found two immediately, the upper limit switch, on the outside of the unit next to the blower motor and the lower switch on the face of the unit next to the pressure switch(which has the rubber tube attached to it). After some internet searches and taking the furnace apart I found the auxiliary switch. This switch can only be accessed by removing the lowest right bottom panel and reaching up into the unit. Upon doing so the auxiliary switch has a reset button in the middle of it, I pushed in the button to reset the switch. Put everything back and proceeded to start the furnace. It started right up and ran for a few minutes then shut down. Error code flashed 3 times, which is, combustion air switch failed to close. Took the rubber tube off and blew in and sucked out on the pressure switch a few times to check the pressure switch opening and closing, which you can hear, put the tube back on the canister above the booster motor and proceeded to start the furnace up. Upon starting I taped the side of the booster motor with a wrench and the furnace fired right up. I hope this helps others.

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