NO Hot Air

[eherz1]

I have a friend who has a Colman furnace Model DGAA070BDTB. The unit seems to function properly but only cold air comes out. The glow plug gets hot and then the gas ignites. After a period of time the fan comes on to send the air through out the house but the air is not hot. I was told that the gas valve was bad and replaced the valve but it still has the same problem. Is there 2 stages to the amount of gas that comes out? It seems that the flames should be a lot more in order to heat the house. I just don't think there is enough gas coming out to produce the amount of heat required to heat the house. Both gas valves did exactly the same thing so I am thinking it is not a gas valve problem. There is plenty of air coming out of the ducts and the unit worked just fine last winter. What could be the problem?

[furnaceman]

since i am not sure of your technical level, let me suggest a few quick things,
are there any flashing codes? if so, what are they.
you'll have to excuse me, but i don't have a manual in front of me at the moment, so i am not exactly sure of the furnace, but i'll try to help.
you say it has a glow plug, so i assume you mean an igniter, if so it will have a control board. on the board should be a led that flashes, count the number of flashes/duration and let us know. there may even be a sticker on the back of the door or board itself telling what the code means.
I am curious how someone came to the conculsion the gas valve was bad before, on a call for heat when the valve is energized(24-28 vac) it should read that voltage continously during the heating call. it is also possible the valve is sticking, you could try rapping it with a wooden handle, but if it sticks once it will again.
you say u changed the gas valve, you might need a tech to adjust the in/out inches of w. c. with a manometer for the proper burn rate, also it is possible that the gas burner/tubing is partial clogged and needs blown out.

[eherz1]

The first thing I checked was for flashing codes and there are no flasing codes. The green light is on and steady. As for a glow plug, yes I am technically advanced but don't know the proper terms, it is an ignitor. I did try rapping on the valve and it did not make any difference. Everything seems to work properly but I don't feel there is enough gas flow to heat the unit up enough to heat the house. There is a lot of flame but I don't think it is enough. A heating repair man said the gas valve seemed to be bad because not enough gas was coming out of it or should I say not enough flame was being produced from the gas coming out of the valve.
I can take the unit apart and see if the gas burner tubing is clogged. At this time, it is the only thing I can figure is wrong with the unit.

[Robert]

Hi,

Inspect inside the main burner orifice and orifice spud for possible clogs (spider/web).


Thanks,
Robert