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My furnace will not stop turning on and off. I have no clue what is going on and am getting a little frustrated. Any help would be great.

Michael

What is the furnace model number ?

Is the blower only or blower and heat source doing this ?


Thanks,
Robert

Robert,

It is a Coleman-evcon model number DGRT070AUA. 70,000
Btu input, 57,000 output.

The blower is the only thing that keeps turning off. The heat source
Stays on throughout cycle. Thanks for all your help.

Michael

Hi Michael,

Fan Switch # 7975 - 3281 is most common fault. You can test by placing one meter lead on each terminal while blower is running testing for 120VAC.

Should read 0VAC while running and 120VAC if it opens when blower stops.

Then 0VAC when blower runs again.


See if the fan switch reads like that.


It can be seen and ordered here by paging down:

http://www.aberdeenhomerepair.com/store ... -7975-3281


Once it starts shortly after burner ignites, it should remain running and you should read 0VAC as long as burner is lit and for a short while after burner goes out..


Thanks,
Robert

Robert,

The fan switch is reading as posted above. If I flip the power switch, wait a couple of seconds, then turn back on, it will run for a longer period of time. Then it will start coming on and off. I have noticed the only time the furnace is having this problem is early in the morning, say around 5:30am. Thanks again for your help.

Michael

Hi Michael,

The fan switch should never open and turn blower off any time as long as the burner is lit and for a short while once burner goes out.

IF it is opening and closing with burner lit, it is either bad or there is airflow getting to it cooling if off.

As for DIY, all you can do is replace it and see.


Thanks,
Robert

One other possibility is that there is a Blend-Air system that is allowing very cold outside air into the return plenum, thus lowering the air temperature to the point of the fan switch's shut off temperature setpoint. Turn off the blend air and manually observe that the outside air damper is actually closed and check for continued cycling of the blower. If it no longer cycles off and on, you know where the problem lies.

Gordo

That would fall under airflow getting to it and if burner flame and heat chamber is producing correct temps, the blend air will not effect it.



Thanks,
Robert