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I have a Coleman Evcon Presidential, mod. # 7995-656/D, with the hot surface igniter that's giving me fits. In order to get it to light, I have to turn the thermostat down and then all the way back up (sometimes 5-10 times). The igniter will light up and glow, then there's a click, then it lights for a second, clicks again, and occasionally it lights back up and stays lit for a few minutes, but usually it doesn't, so I have to go through the whole process again. Then...when I get it lit, it only stays lit for 3-4 minutes and then shuts off. It started giving me a little trouble this year when we switched it to heat, but now it's almost impossible to keep it going enough to heat the house. If anybody has any idea what's wrong or what I can do to figure out what's wrong, I'd greatly appreciate it. Thanx.

I'm far from a furnace guy but almost sounds like a flame sensor issue to me.

I'm with Ponch as far as an expert, But as cold as it's been I think I would call one. The newer furnaces have many safety interlocks, any one of them could cause the problems. The problem is finding witch one.

Greg

Take the flame sensor out, I think it should be like a rod type and then you can try cleaning it with sand paper and re-install to see if it improves.

Thanks y'all. I'll try sandpapering the flame sensor. If that don't help it, I'm probably gonna have to call a pro.

Well, so much for cleaning the flame sensor...there isn't one! I'm thinking it's either the gas control valve or the ignition control module. Just not sure now to test them. Looks like time to call a pro.

Do you have a wiring schematic available? There's gotta be a flame sensor. Is there any other model number info you can provide like is a DGAT or DGAM? I believe I have a manual downloaded somewhere for this series.

Or post a picture of the burner unit and what's around it. My flame sensor is "built into" my burner unit. Meaning I have to take the whole burner unit out to clean it. But that is just undoing the gas piping at the union and then a half dozen or so screws and the whole thing pulls out.

If you go to this google image search and look at the two pictures in the second row(happen to be from this site!) you will see what my burner assembly looks like. The thing that the two white wires goes to is the flame sensor. I have to clean mine every few years. Maybe your's is something like this?

I couldn't find a flame sensor listed on either of the factory schematic stickers either. I tried to post pics, but it says the file size is too big. My burner assembly looks like the: Product ID: F-1021-32/Coleman Burner Assembly (7970-5851/A) pic on this page: http://www.mhparts.com/coleman-evcon.php?pg=3 except that it only has the 2 white wires (no yellow wire) and no flame sensor. Other than that, it looks exactly the same. I appreciate y'all's help.

The igniter on your furnace becomes the flame sensor after the voltage is cut after igniting the burner. Check the main burner orifice for a spider web.

Thanks DaleM. That was a problem when we 1st moved in here, so I've already checked that this time.

One other thing I run into on the 7900 series furnaces is the degradation of the inner flue pipe on the roof jack assembly. As the pipe rusts internally the rust falls onto the upper damper of the heat exchanger and blocks it. This causes flue gases to build up as they are unable to escape. The flow of combustion air is also cut off as it is a concentric flue system. Once the problem gets real bad the inner pipe begins to rust away and develop holes. These holes allow flue exhaust gases back into the fresh air intake portion of the roof jack assembly. This inturn limits the amount of fresh air coming in, the burner flame dwindles and gets shut down by the flame sensor/ignitor.

DaleM wrote:One other thing I run into on the 7900 series furnaces is the degradation of the inner flue pipe on the roof jack assembly. As the pipe rusts internally the rust falls onto the upper damper of the heat exchanger and blocks it. This causes flue gases to build up as they are unable to escape. The flow of combustion air is also cut off as it is a concentric flue system. Once the problem gets real bad the inner pipe begins to rust away and develop holes. These holes allow flue exhaust gases back into the fresh air intake portion of the roof jack assembly. This inturn limits the amount of fresh air coming in, the burner flame dwindles and gets shut down by the flame sensor/ignitor.

...And that is why it it important to at least talk to a pro, that is something that only experience can bring to the table.

Greg

Thanks again DaleM. It's getting us by, as long as we "babysit" it, but as soon as I'm able to get a pro to look at it, that's what I'm gonna do. I've got no problem doing it myself, if I can get it figured out. But, I also know when something's "over my pay grade". lol