no heat from suburban furnace

[David Carrol]

furnace worked day before yesterday than Yesterday evening I kicked it on but could get no heat. The fan comes on and runs for a few moments then goes off. I can turn the furnace off and back on and the process repeats. I took the cover off so that I could get to the furnace but really didn't gain much. I can see the motor and that is about all. I had my wife cycle the furnace while I watched............. It attempts to ignite; I get a blast of hot air out the exhaust but it does not sustain.



Does anybody have a suggestion.

[prairieschooner]

Here is a link to a previous discussion;
http://www.luxurycoachlifestyle.com/forum/hvac/1722-suburban-nt-12l-16l-furnaces.html

I had to replace the Thermocoupler on one of mine and another required a new circuit board. I bought one from Dinosaur Electronics. I just called them to get the proper circuit board and it works much better than the original;
Ignitor Board Index page (http://www.dinosaurelectronics.com/Ignitor_boards.htm)

[Newell Attack]

Suburban has a thermocouple that keeps the pilot lit after the timer tries to shut the gas valve off. To do that it is positioned in the pilot light flame and if it is warm enough it holds the gas valve open.

If you are getting heat for a brief period of time the thermocouple is probably not getting hot enough. It may be bad but probably just needs to be repositioned to get more heat from the pilot light.

[The Newell]

When the fan starts do you hear a clunck shortly after? If not your gas valve probably isn't opening. Could be a board problem.

[David Carrol]

No I don't hear anything like that, I'm hoping it's a minor thing, like a small wasp nest stuck in the sail switch or something. Boards are not cheap.

[David Carrol]

I talked with Newell and they think there it is too much butane in the tank and claim that down in the south they mix a lot of butane with the LP. According to them when it gets as cold as it has been here the butane just won't work.

Thought I would share,

David Carrol

[77newell]

David: the logic in the control boards I've had for my Suburban furnaces goes as follows: fan kicks on - then sail switch checks air flow and timer runs to ensure no fuel is left in furnace - when timer times out the igniter starts sparking and gas valve opens (I can usually hear the sparking when the front of the furnace is open and usually hear the gas valve open) - then the board checks for flame and a timer will shut things off if no flame detected after a short period- furnace continues to run until thermostat circuit opens then everything shuts down.

Butane will vaporize down to about 34 degrees, depending on the mix with propane you may get lower and still get gas.

[The Newell]

Thanks David, We appreciate the update.

Well, they DO mix a lot of butane down south and yes, it does not vaporize as well in very cold weather. Some blends may be as high as 70-80% butane. Butane boils at right around 30 degrees F., so pure butane wouldn't be worth much on a cold night. Propane boils at something like -100 F and a mix of the two boils off somewhere in between. Plus, I suppose drops of liquid butane might condense out on very cold surfaces, though, and maybe that causes problems in the burner tube or orifice on extreme cold nights.

[prairieschooner]

Hey we all have an opinion.......go to the Troubleshooting part of the Owners Manual and follow the suggestions. That is what I did.