[quote=wacnstac]Well I thought I was going to have this problem licked. I had the furnace on my bench and found that the limit switch which is normally closed was open. I ordered a new limit switch, fan switch, and sail switch, for good measure.
Replaced them all, cleaned things up a bit and hooked up to gas (with a brand new regulator) and hooked it up to power. Then I fired it up by putting 12V
on the thermostat connector pin. The fan turns on, the sail switch engages, and about 10-15 seconds later, the gas solenoid pops open (audible click) and I get a good spark from the ignitor for a good 5 seconds. ]
You know, on re-reading this thread, something bothers me. When I bench test a furnace after an overhaul, cleaning or repair, I use the pigtail that plugs into the igniter board as follows:
red to +12VDC
yellow to -12VDC
I then use a jumper between the 2 blue wires (thermostat) to turn the unit on and simulate a call for heat from the t/stat.
This is how your furnace is connected in your trailer. There is always power to the board, but it is the thermostat that acts as the on/off switch depending on it's setting and the ambient temp in the trailer.
I get the feeling that you powered the board by directly applying 12VDC to the t/stat wires. This is not recommended, as it is a control source and not a primary power port for the igniter board. It might have done strange things to the board and might have been the source of your explosion by not allowing the unit to properly purge before igniting.
If you ever
have any questions about how to bench test a furnace, water heater or any other component in your trailer or MoHo, PLEASE CONTACT ME!!!
We want you around a little longer and sure don't want to be reading your obit or hear of a serious injury that wasn't necessary