Coleman furnace Model- DGAT075BDC Serial- 941057861

Questions about repairs and parts for Coleman furnaces, air conditioners and heat pumps for manufactured homes. Click here for Coleman parts.

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Joe 1
Posts: 4
Joined: Mon Feb 20, 2012 8:28 pm

Mon Feb 20, 2012 8:41 pm

I have a Coleman furnace Model- DGAT075BDC Serial- 941057861
The problem is - the furnace will operate just fine for a sporadic period of time. Parts that have been replaced are as follows; flame sensor, igniter, thermostat, HS 780 34 NR-306 ignition control & the inducer assy.
After all this it still sporadically goes into lock-out. All wiring connections from the supply power thru the relays & low voltage have been checked & rechecked.
When the ignition control was installed, a sort of dedicated ground was installed from the ground terminal on the box to the case (the yellow ground for the 24v. was on this same terminal. 121.6v. to furnace, 26.59 out of transformer....help PLEASE?


DaleM
Posts: 385
Joined: Wed Apr 07, 2010 10:07 am

Tue Feb 21, 2012 3:21 pm

If you can view the flame while in full burn, see if it goes out at full burn or does it dwindle to a small blue only flame then go out? If dwindling to a small flame you may have either a partially blocked flue vent or holes in the inner pipe of the flue assembly causing the unit to recirculate flue gasses, thus not enough fresh air to support proper combustion.

Joe 1
Posts: 4
Joined: Mon Feb 20, 2012 8:28 pm

Tue Feb 21, 2012 6:19 pm

Thanks for the information, thats exactly what I'll try next...if you happen to think of something else please share...I appreciate the help!

Joe 1
Posts: 4
Joined: Mon Feb 20, 2012 8:28 pm

Wed Feb 22, 2012 7:22 am

The flame snaps off each time it goes out, no dwindling....the wierd thing is I can't catch it because it may do this "lock-out" once a week or a couple of times in a day. It's really frustrating.

Joe 1
Posts: 4
Joined: Mon Feb 20, 2012 8:28 pm

Wed Feb 22, 2012 7:22 am

The flame snaps off each time it goes out, no dwindling....the wierd thing is I can't catch it because it may do this "lock-out" once a week or a couple of times in a day. It's really frustrating.


DaleM
Posts: 385
Joined: Wed Apr 07, 2010 10:07 am

Thu Feb 23, 2012 12:19 am

You have a flame sensor and igniter? Three wires coming out of the burner area, 1-yellow and 2-white, correct? Yellow is to the flame sensor and the 2 whites to the igniter. If I'm not mistaken there should be a small metal tab at the end of the burner assembly at about the 3 o'clock position, small maybe 3/8" wide by a 1/4" long, bent like a tongue hanging out of a mouth. If it's there shine up the end of it with a bit of emery cloth. If it's NOT there shine up the lower end of the burner assembly, not the target/flame deflector. The flame sensor works by measuring the amount of millivolts passing from it to ground. Apparently those millivolts flow better through a flame and that is how it senses to keep the burner going after igniting. Those little tabs get rusty or rust off and fall away and the flame sensor senses no flame and cuts the burner off. If you're not sure what I'm talking about I can take a pic of a burner assembly I have, provided I still have one for that model unit.

Another thing you can do is clean the flame sensor. Light steel wool or a scuff pad will take care of that.

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