Furnace help

Milemaker you are correct mine also starts with a signal from the thermostat. This starts the fan, the sail switch then closes to power the ignition board. At shut down the fan runs a cool down cycle. When I took the RV in to have the safety check done the tech told me that the furnace lit but the fan didn't come on and offered to pull it for a fee of $150.00-$300.00. after getting a set of prints thanks to Tiger4x4RV I too thought it odd It would light but after pulling the unit I feel like the sail switch most likely was stuck closed. I pulled all the switches and found the fan switch was sticky as well but working. I tested them over a light bulb. this led me get all new switches. The main problem was the mechanical Time delay relay. one of the coil wires appeared to have come in contact with the metal case causing a short circuit and burnt the wire into. This and a stuck sail switch allowed the furnace to ignite and the fan remain off. I bought two relays,fan and limit switches. So now I have a complete set of spares I hope I wont have to use.

Glad you got it sorted. I was confused by this though:

This old heater has signs of never being lit, it comes on OK but the fan does not come on.

I'm not sure why it would "come on" if the fan is not running. With my furnace (circa 1990) the fan turns on first, and then the furnace lights up. After the thermostat shuts down the flame, the fan continues to run until the unit is cooled off.

There shouldn't be any fire burning unless the fan is running, as far as I know. That's why you have a sail switch - it should prevent the burner lighting off if there is no airflow through the furnace, to prevent it from overheating.

Steve

Just a line or two to thank every one for their help on my old Travel craft's suburban furnace. shes back up and purring like a kitten.It's a ducted unit and pours on the heat.Now I'm looking forward to the thanksgiving outing I have planed for the boys and I. Thanks again.

Well I finally pulled the furnace from the Travel craft and cominced to trouble shoot my heater problem.My hunch was a bad fan switch so i started with a continuity test through the fan circuit the two disk switches I pulled and read with a meter while using a lightbulb as a heat source opens and closed as they should however the fan switch was a bit sloppy at first.the sail switch was found to be good as well. The fan motor spins free so I went back to the trusty print and read the circuit through the thermostat switch and found that the coil wire that pulls in the fan circuit had burnt into right at the spot where it leves the coil.So good news is I found the problem. Bad news, part is no longer available,but thank goodness there's eBay.I found it there and bought two of them. As soon as they get here I'll get it up and running;that is if the ignighter board hasn't got a fault. Thanks again for all the info given me on this essue.

Thanks bordercollie the furnace ignites ok but the fan won't blow, Im going to go at it tomorrow. One of the problems is its 35 years old and was never used. There's no sign of it ever being lit so I'm thinking It's a simple problem. Hopefully not a batch of dried out capacitors on the board. hopefully as you said a sail switch or bad connection. Maybe just need to give the motor a spin to clear corrosion from the commentator segments.

Just a quick suggestion, check 12 volt wiring to furnace. May have a loose or corroded connection to positive 12vdc or ground that would explain no blower.Check for 12.6 volts or more at furnace connection. Other common problems are stuck or defective sail switch, air bubbles in propane lines, no spark ignitio/need to clean contacts on circuit board, obstructed exhaust outlet. Old furnaces can be stubborn about starting and cycling with thermostat settings and touchy safety features. Start up procedure must be followed.

Wow ask and ye shall receive.Thanks for the quick replies. I had searched for info on the net but only found bits and pieces of what I was looking for. This old heater has signs of never being lit, it comes on OK but the fan does not come on. Thanks for the links. Tiger4x4RV your link was just what I was looking for Thanks for everyone's input I'm trying to get my old girl up to par, the furnace was the only thing that wasn't working when I brought her home and the only thing that didn't have documentation go figure. again Thanks!!

Owner's manual for that model is online:
http://www.gmcmi.com/wp-content/uploads/2014/05/Suburban_Dyna-Trail.pdf

It would be helpful if you told us what problem you are having.

The best collection of Rv service documents online is at http://bryantrv.com/docs.html. Start your search there.