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Richard, Technical Manager
Category: HVAC
Satisfied Customers: 1514
Experience:  27 years of Experience, NATE Certified, professional trainer
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Im am getting the 3 flashing light code for [Coleman Furnace]

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I'm am getting the 3 flashing light code for [Coleman Furnace] Air Pressure Switch 024-27666-000 -0.15, the replacement part number, my part is still 0.20.
Can I assume this is the problem or could there be a problem in the flue, where the combustion blower motor is, or some kind of exhaust valve that is not working.
I've taken the switch out, checked everything else on the furnace that I could. It is turned on, I get the 3 green flashing light code. This part of the flue(?) that the vacuum tubes connect to is getting hot, but it isn't clicking to ignite. I'm assuming that the combustion blower motor is in there, too.
Will replacing the air pressure switch correct this. The unit had been turned off for heat for about 6 months and worked perfectly last season. The air conditioner still works fine.

Hello you will be wasting your money replacing the switch. They very rarely go that far out of calibration. The only way to know for sure is to measure the vent pressure with a gauge. However what I would do it check the vent for blockage take the draft motor out and make sure nothing got in there. You could have a blocked flue or bad vent motor or restriction in the heat exchanger. The blocked flue or something in the vent motor will be your most common causes. .

Let me know ,Richard

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Customer: replied 5 years ago.

Ok I appreciate the answer although I am a novice, just to clarify, clear the flue/vent, make sure there are no restrictions.
Terminology: is draft motor and vent motor what they call the combustion blower motor in the flue?
What exactly is the heat exchanger, and is that in the flue or in the combustion chamber?

Thank you

hello yes the draft motor or sometimes called combustion motor, vent motor are all the same thing. The heat exchanger is where the burners light and go into. Air moves over it causing heat to exchange from the hot heat exchanger to the cool air.