Coleman DGAA07OBDTA

[staylor63]

Hello Gentlemen,
I have this unit installed in my garage. It has run great for a couple of years now. This winter though i am finding it pretty much comes on and shuts off when it wants to, usually running at night. I tried taking the t-stat off and just jumping the wires, but no go.After i turn the unit off and power it up, it goes thru the normal start up sounds but then wont fire up and i have 2 flashes on the indicator light. sounds like an igniter but am not sure. Can it be too dusty? The intermittent problem has got me on this forum....any help would be great!
Steve

[gordo48111]

If you look on the control box cover behind the top panel, there should be a diagnostic code chart to tell you what the two flashes indicate. On my DGAT model furnace, two flashes indicate the centrifugal switch on the combustion air blower motor housing is stuck open.

[Robert]

Turn furnace off or set t-stat for a no-call for heat. Take a volt meter set for ohms/resistance testing. Remove one wire from pressure switch and test across for continuity.

Pressure switch is round disc shape with 2 wires and 2 tubes attached mid way of furnace.


2 flashes is pressure switch failed closed.


Thanks,
Robert

[staylor63]

Thanks for the insight Robert, when I test the switch is it normally open or closed?
Steve

[Robert]

Hi Steve,

It is N.O. and should open at end of each cycle. Your diagnostic code is saying it is staying closed.

You should not have continuity once it is off. Testing will verify the flashing code. By the code, it should show continuity if it is indeed stuck closed.


Thanks,
Robert

[staylor63]

Hello Robert,
After testing across while furnace was off, the switch was open, i had no continuity. could it be the switch works intermittantly?

[staylor63]

Robert,
Here is the latest i have found. Turned on furnace, blower motor goes on, some clicks from the control board. More clicks and the ignitor starts glowing. 5 seconds later ignitor stops glowing. It repeats this cycle a couple of times and then shuts down leaving the indicator light blinking twice.
Any thoughts?

[Robert]

Need to be checking at ignitor wires for 120vac from call for heat until ignitor goes out. See if it gets the 120vac within 30 to 45 secs. or so and then does it lose the 120vac when it goes out after just 5 secs. glowing ?


Thanks,
Robert

[staylor63]

Robert,
I just tried starting the furnace 10 times. 8 of the times the only thing that came on was the draft inducer motor, then 2 flashes on indicator. 2 times though after about 15 seconds of draft inducer running I heard a click and the ignitor started getting 120vac to the wires. after about 20 seconds it started glowing red then i heard another click like it was time for flames to start but nothing and after 2-3 seconds the ignitor stopped glowing and it stopped getting 120vac to it. then i am looking at 2 flashes again and back to square 1.

[Robert]

Make sure booster motor and wheel are clean and running good. Make sure air pipe to motor is not leaking and not loose , damaged or clogged.

Make sure the tubes from motor to switch are not clogged, loose or kinked.


Make sure there is always 24vac to one of the two pressure switch wires.


IF so and pressure switch never closes (should read 24vac across terminals and read 0vac when it closes).

IF it does not close, will need to call an hvac tech. Could be a few things wrong and will need testing to determine which one.


Thanks,
Robert

[staylor63]

Thank you for all of your help Robert, you have got a great business model here.
Good Luck with everything...

[Robert]

You're very welcome, happy to help.


Take care and best wishes,
Robert