Coleman DGAH077BBSB blows cold air

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Coleman DGAH077BBSB blows cold air

Postby 2hightech » Sun Oct 03, 2010 11:56 am

Hi, I've been to your forum in the past but never posted - great site!

Anyways, I have a Coleman furnace in my mobile home - P/N DGAH077BBSB - which was installed professionally in April '07. It worked fine until last winter when the pressure switch failed (error code: flashed 3 times and would not light).

I replaced the pressure switch with P/N 9371DO-HS-0031, which is a 0.18 aperture switch (replaced the 0.15 switch in there previously). Furnace ran fine after install, but only used a couple of weeks until the weather turned warm and hasn't run since.

I installed new box filters on the door this week (before running the furnace) and then turned up the thermostat for the first time this week, and it has only blown cold air since. I checked for error codes and it indicates steady green. I can see the ignitor lighting, the burners lighting, and after about 30 seconds the blower comes on - but only cold air comes out. This cold air even comes out of a heat vent located approximately 3 feet from the furnace.

Can anyone help guide me as to what the problem may be?
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Re: Coleman DGAH077BBSB blows cold air

Postby andyr78 » Sun Oct 03, 2010 8:18 pm

I've had this happen before. Our pilot would light, but from what I understand it would not light all the way and would blow cold air. We had spiderwebs in the gas valve preventing the correct amount of gas from entering the furnace. I called someone out once, but after watching him do it. I think it would be a fairly simple procedure to do myself if it happens again. After shutting the gas off, he took the valve assembly off and cleaned it out with what looked like a long handled q-tip.
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Re: Coleman DGAH077BBSB blows cold air

Postby 2hightech » Sun Oct 03, 2010 10:43 pm

Thanks for your response. I found the following info useful http://www.ehow.com/how-does_5045697_troubleshooting-coleman-furnace.html and it mentions dirty burners being one of two possible causes for blowing cold air. Since my furnace does start and run apparently properly (the pilot lights the burners just fine) I would have to say that the problem lies in dirty burners. I'll investigate more tomorrow.
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Re: Coleman DGAH077BBSB blows cold air

Postby Robert » Mon Oct 04, 2010 12:28 am

What does the burner flame look like ? Is it strong ? Don't believe everything you read/see on those ehow things.


Could be dirty burner or spider/web in the burner orifice causing low burner flame and low heat.

Could also be a disconnected duct boot or the duct itself near the furnace allowing heat loos and entrance of cold air.



Thanks,
Robert
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Re: Coleman DGAH077BBSB blows cold air

Postby 2hightech » Mon Oct 04, 2010 8:08 am

Thanks for the reply, Robert, the flame looks short and weak with a purple flame. It almost appears as if when the blower goes on that the flames are being knocked around to the point they will extinguish (but they don't).

The front face of the chamber is labeled "HOT" yet it is barely lukewarm, even after running for several hours.

The cold air comes out of every single duct in the house, including one literally 2 feet from the furnace. The underside of the home has been insulated pretty well with foam-type insulation, I'd have to remove a foot of insulating foam from around the ductwork in order to inspect it.

Thanks for the info!

edit: oh, and I forgot to mention this (not sure if important) but every season when the furnace was run I could smell the furnace itself heating up - that "hot metal appliance" smell. Well, I can't smell it this season at all, smells cold.
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Re: Coleman DGAH077BBSB blows cold air

Postby Robert » Tue Oct 05, 2010 12:32 am

Inspect the burner orifice for spider/web and also inspect the burner tube for clogs.

Remove floor registers. Start at one end of home, lay bright light down in duct aiming toward next register. Go to next register and hold a mirror down in duct looking back at light.

Keep doing this to inspect the entire duct.

IF you have a digi camera, lay it down in duct and take pics of certain areas.

Load pics to computer and enlarge them to see duct up close and personal.



Thanks,
Robert
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Re: Coleman DGAH077BBSB blows cold air

Postby 2hightech » Tue Oct 05, 2010 5:52 pm

Thank you so much for the replies and help, most appreciated!

I disassembled and inspected the burner tube/orifice and the entire unit was very clean, but I blew it out with compressed air to be sure. I also inspected the gas valve orifice and found no debris/blockage. Upon reassembly I do find the flame appears stronger/more full, with nice blue flame. However, it still blew mostly cold.

I then opened up the heat register nearest the furnace (roughly 2' from furnace) and found a roughly 1'x2' hole - basically the whole bottom/sides of the duct are gone below this heat register! I believe this was caused by a pet cat we used to own that would only use that spot for bathroom duty (GRRRR). Basically the duct is no longer there, furnace blows directly into the subspace below the home. I will be trying to repair this tomorrow using cardboard and duct tape (temporary fix until I can locate some sheet metal) and I will report back upon completion.

Your tip on the camera to inspect the duct was spot on - it let me see past the register in both directions to find the rest of the ductwork appears fine, but I will be inspecting the rest of the home soon from other registers.

thanks again!
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Re: Coleman DGAH077BBSB blows cold air

Postby Robert » Tue Oct 05, 2010 11:46 pm

Hi,

You're very welcome, happy it helped .




Thanks,
Robert
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Re: Coleman DGAH077BBSB blows cold air

Postby 2hightech » Thu Oct 14, 2010 11:03 am

Update:

I had to leave town for a few days on business and didn't get the chance to repair the ductwork until today. I did not have any sheet metal, so I used some stiff corrugated cardboard (which is much thicker than the duct sheet metal actually). First I filled in the areas around the duct with insulation, then placed the cardboard across the hole, and finally taped all the edges together with duct tape for a secure airtight (so I hope) fit.

The result? I ran the furnace for about 2 hours now, and it still feels cold.

I checked the rest of the ducts by using the camera trick used earlier, and I can't see any other openings which need repaired.

I set a digital thermometer up in the living room, and when I first turned on the furnace it was 67 degrees; after 2 hours of the furnace running it is now 63. The furnace runs continuously, no breaks.

I would love some help with this, don't want to have to call anyone in unless I have to. I'm an auto technician by trade and this doesn't seem beyond me if I have some direction.
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Re: Coleman DGAH077BBSB blows cold air

Postby Robert » Thu Oct 14, 2010 1:18 pm

Remove the duct tape, cardboard and insulation and repair it right. Get some sheet metal or aluminum, pop rivet it in place, cover seams with foil tape, then cover all of the patch with mastic duct sealant.

Make sure all of duct is sealed and all of belly is sealed.



IF all of duct is done and burner and burner orifice is clear, time to call an hvac tech.



Thanks,
Robert
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Re: Coleman DGAH077BBSB blows cold air

Postby 2hightech » Thu Oct 14, 2010 2:31 pm

Will do. Thanks for the help.
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Re: Coleman DGAH077BBSB blows cold air

Postby Robert » Thu Oct 14, 2010 8:49 pm

You're very welcome, happy to help.



Thanks,
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