Suburban furnace troubleshooting help

[Smann316]

I recently bought a used trailer and it has a suburban sf-25 furnace in it. It sat unused for a long time so I brought it home, cleaned it out, powered it up, connected propane and it worked as it was supposed to. I was elated. Went back down an hour or so later just to confirm I was good to go and it's not firing. Blower works, but it is not "clicking". There is nothing from the igniter. I tried several times. The sail switch appears to be working. I assume they can go bad. How do I know if it is bad? Any suggestions or help is more than appreciated.

[ksg5000]

Welcome to RV World. B4 RV my mechanical skills were limited to duct tape and hammer. Glad you resolved your problem.

[Smann316]

So I replaced the sail switch and apparently that was the culprit. Replaced it and tested the unit a couple of times and it functioned perfectly.

[ksg5000]

The way I test any switch is to use simple continuity test - turn the switch on/off ... when "on" the switch will register continuity.

Is your rig plugged into shore power? Furnace blowers require good power source to maintain enough revolutions to keep the sail switch open.

[dougrainer]

ALL the sail switch does is close to allow 12 volt positive thru it. You test the sail switch by just seeing if when running you have 12 volts on both wires at the sail switch. IF NOT, and you have 12 volts on one side and not the other the switch is bad. Doug

[Smann316]

I checked my sail switch and tell me what you think. I started the blower and it ran fine, still no spark. In an effort to test the sail switch i touched my multimeter red to red black to black. The meter "jumped" and then showed nothing. Then my furnace sparked and started up. I did this 3 times in a row. This tells me that sail switch is bad. Am I correct?

[Chris_Bryant]

The most common failure I see in this model is the limit switch, which can be accessed from inside the trailer- remove the inside panel and it's right there. The tabs for the quick connects get oxidized, you can often fix it with a pencil eraser, or sometimes just disconnecting and reconnecting will do it.

[ksg5000]

Is the rig connected to shore power? If not check the battery -running the furnace blower consumes battery power and when the battery starts to deplete the blower slows down eventually closing the sail switch. Also - double check that you have sufficient propane.

[Mandalay_Parr]

First verify you have good 12volts at the furnace. It should be above 12.2 volts for good fan operation or sail switch won’t activate.

[Old-Biscuit]

Yes sail switch MUST CLOSE in order for DC Voltage to go to circuit board

No DC thru sail switch then no DC Voltage to gas valve/spark electrode

Sail switch makes up when fan motor reaches 75% RPM.....dirty switch, dirty 'paddle' etc ----sail switch doesn't make up

Check for 12V DC at sail switch....both sides
Black wire to ground (DC to sail switch)
Red wire to Ground (DC from sail switch going to circuit board WHEN switch is closed)

YELLOW wire is ground source