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IUFAN87 12-30-2011 03:31 AM

Coleman furnace problems
 
I have a coleman furnace model #DGAT090BDD. My roof leaked water onto it and damaged the high limit switch and the control module. The green LED on the module was flashing rapidly. I replaced both the module and the limit switch. The furnace worked fine for a few days. But it started doing the rapid flashing of the LED again. I can manually cycle the power off and back on and sometimes it works fine for about 24 hours. But cycling the power off and back on doesnt always help. Sometimes as soon as I cycle the power switch it starts the rapid blinking again, and the furnace wont function. What could be causing this?

beenthere 12-30-2011 04:21 AM

Count the flashes, they are an error code. then look at the code legend and see what it says.

IUFAN87 12-30-2011 07:13 AM

Quote:

Originally Posted by beenthere (Post 807098)
Count the flashes, they are an error code. then look at the code legend and see what it says.

Thanks for the reply. But this is not like a typical error code. There is no discernable "blink" of the LED. It actually isnt an "on/off" blink. Its more like a constant bright/dim, and very rapid flash.Thats what I dont understand about it. It has had diagnostic codes I have repaired in the past. One was for automatic ignition failure one time. The other was for limit cycling. Which has happened several times.

Doc Holliday 12-30-2011 07:34 AM

check the transformer. Pull the transformer wires off of the control board and with power to the transformer see if it's putting out a steady 24 volts. It may be fluctuating, going bad due to moisture contamination.

Don't let the wires touch any metal or you will need a new one. :)

Doc Holliday 12-30-2011 07:36 AM

Actually you don't even need to pull them off (risking chance of yourself getting electricuted and yes, 24 volts stings a bit), simply check across the R and the C terminal on the board for a steady 24 volts.

Doc Holliday 12-30-2011 07:37 AM

I'd also check the high voltage coming into the furnace. Start with the basics.

harleyrider 12-30-2011 09:02 AM

Quote:

I have repaired in the past. One was for automatic ignition failure one time. The other was for limit cycling. Which has happened several times.
Sounds to me like you have a much bigger problem......That limit is a safety device that trips when the furnace has reached a dangerous temperature. just replacing the limit is NOT how you address a tripped limit.....you must determine why the limit is tripping, then correct the issue.

IUFAN87 12-30-2011 09:08 AM

Quote:

Originally Posted by harleyrider (Post 807222)
Sounds to me like you have a much bigger problem......That limit is a safety device that trips when the furnace has reached a dangerous temperature. just replacing the limit is NOT how you address a tripped limit.....you must determine why the limit is tripping, then correct the issue.

I should have clarified on the limit switch code i was getting. My roof has leaked on different occasions over the years. The water damaged the high limit switch which set the limit cycling code. Thanks

IUFAN87 12-30-2011 10:28 PM

Quote:

Originally Posted by Doc Holliday (Post 807173)
Actually you don't even need to pull them off (risking chance of yourself getting electricuted and yes, 24 volts stings a bit), simply check across the R and the C terminal on the board for a steady 24 volts.

Just almost like clock work the green LED started the rapid flashing again this evening. Checked the voltages in and out of the transformer. Steady 27 out at the transformer and steady 120 in. As soon as I cycled the power switch off and back on the furnace kicked on and worked normal. Anymore ideas would be appreciated. thanks

beenthere 12-31-2011 03:36 AM

Check you line voltage grounding.

sleepyg 12-31-2011 08:08 AM

If you can "power cycle" (turn off the main power) the unit and it runs some of the time and other times it does not, then I would lean toward having a bad limit or the board is bad.

When you drop the power you release all the electronics to a normal state. When you make the system "call" for heat you start a sequence and when the sequence is not completed you get your flashing light. Use the wiring digram and trace the sequence of how it should start and if it goes to the control board and stops then what on the board stopped it? Could be the limit or could be a bad relay on the board.

Was any moister left behind after you installed the new parts? A little water will do a lot of damage to printed circuit boards.

Sorry for the long reply.

IUFAN87 12-31-2011 09:09 AM

Quote:

Originally Posted by sleepyg (Post 808087)
If you can "power cycle" (turn off the main power) the unit and it runs some of the time and other times it does not, then I would lean toward having a bad limit or the board is bad.

When you drop the power you release all the electronics to a normal state. When you make the system "call" for heat you start a sequence and when the sequence is not completed you get your flashing light. Use the wiring digram and trace the sequence of how it should start and if it goes to the control board and stops then what on the board stopped it? Could be the limit or could be a bad relay on the board.

Was any moister left behind after you installed the new parts? A little water will do a lot of damage to printed circuit boards.

Sorry for the long reply.

Thank you for the reply sleepyg. It was completely dry when I installed the new board and hasnt gotten wet since. Like I said it worked fine for a few days. Sometimes I can cycle the power and it will start working. At the moment it is not working. I cycle the power switch and it continues the rapid blinking. I will do some more troubleshooting. Thanks so much for the advice.

Doc Holliday 12-31-2011 02:42 PM

I'd remove the thermostat from circuit when diagnosing.

IUFAN87 12-31-2011 04:10 PM

Doc, are ya thinkin the t-stat cud be the problem? Because last night I woke up and it was cold in the house. I checked and the LED wasnt blinking. I checked the thermostat. It was set at 70. So I pulled it back til I heard it click. Temperature was at like 58. I then heard the furnace start working.

Tator1076 12-31-2011 04:17 PM

You may have stat problem but some of those units if it went out on lock out and once you cut the unit off by tstat or switch it will reset board. Also that may have a smart valve gas valve on it.


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