Coleman furnace- no ignition

Chris · Mon Sep 24, 2012 7:47 pm

heres my fun: have a mobile my wife and i purchased a few months ago with a coleman furnace with electronic ignition. the model number is DGAA056BDTA The a/c side of things runs great, and we were assured the heat works as well, however when we attempted to use the heat, there was no ignition. im convinced the problem is either the gas valve, the ignitor, or a voltage/signal problem causing the valve or ignition to fail. unfortunately, im having trouble understanding the flash codes as when the unit is first powered up, both the red and green lights alternate between flickering rapidly, and steady on, then after about 30sec, both lights go off and the unit does nothing else. any ideas or troubleshooting thoughts would be much appreciated

DaleM · Mon Sep 24, 2012 11:17 pm

Forget about flash codes for now. Here's a quick way to diagnose your furnace problems. This is based on having a known good board in the furnace and eliminates the thermostat in the troubleshooting process.

First kill power to the furnace. Next locate the red and white thermostat wires at the furnace. Disconnect them and wire nut the red and white from the furnace together, not the wires from the thermostat, just let those hang for now. Turn the furnace ON. Sequence of events is as follows: 1. combustion motor turns on. 2. pressure switch closes. 3. igniter glows. 4. about 30 seconds later gas valve opens and burner fires. 6. about 45 seconds after burner fires the blower comes on. If all this happens accordingly the problem is in the wiring to the thermostat or the thermostat itself.

If nothing happens when you restore power to furnace then you have to check for power to the board and that the transformer is supplying proper control voltage (24vac).

If this sequence is interupted at any point that is where your problem is. Example: combustion motor turns on and pressure switch closes but igniter fails to glow igniter is bad. Best to disconnect igniter and verify voltage during start up procedure (step 3 above). If voltage is present, replace igniter.

Hope that gives you a starting point.

Chris · Tue Sep 25, 2012 7:55 pm

I was a bit doubtful about the thermostat failing after similar issues with the propane converted dryer in our old house, but tried it and nothing. Appreciate the help with the starting point tho, helped confirm what I was afraid of. Do you happen to know which wires are the incoming power to the board? or which wires are exiting the transformer? I haven't yet been able to find any kind of schematics or details that describe where I need to be checking from. And thanks again.

Chris · Tue Sep 25, 2012 8:07 pm

Ok lol nm.. popped the cover to the board and answered my own dumb question. Reading normal fluctuation between 26.3v and 26.6v. from the transformer. Would there be proper voltage if the board wasn't receiving power? and if so do you know which wires are supplying power to the board? there's a green light lit on the control board, but i build computers on the side and know most motherboards will still display a lit power led even with the manual power switch on the power supply shut off, until the power cord is physically disconnected. also i noticed an area on the control board that almost appears singed, where the board is an off-white, there is an area the extends from roughly 1/2" below the fuse, to 1" below the fuse, where it is a redish brown that appears to be a possible board failure. any thoughts?

DaleM · Tue Sep 25, 2012 9:45 pm

If you look closely at the board, all the terminals are labelled. Power will still feed the transformer whether the board is good or bad. The board requires 110v and 24v to operate. I'd pull the board and inspect the flip side of it. If you see a definite buned area it's mostly the failure. That control voltage is fine, as long as you're reading 24+ it will be okay.