RV Repair: Suburban RV Furnace SF-30F, keystone sprinter, suburban furnace

Question
QUESTION: Thom, I own a Keystone Sprinter with a Suburban Furnace SF-30F.  It is Thermostat controlled for both A/C and Heat(Duo Therm).  I operated my furnace on batteries last night and I think I burned out the ignition switch.  In the middle of the night I smelled like an electrical burning smell.  I know the furnace lost power in the night. I heard like a clicking coming from the furnace like it was trying to ignite. I turned off the furnace but in the morning when I had reached the RV park and plugged in, the furnace blower would start but there would be no ignition and the blower would shut down.  


ANSWER: Alex

Well...if the furnace fan motor comes on, then the t-stat is sending a signal to the board to run and not technically defective. The furnace part of the t-stat is just a two wire switch.  The t-stat tells the fan relay to spin the fan,that blows the sail switch, the sail switch sends a signal to the control board to open the gas valve and send spark to the spark probe at the same time. I don't know what you could have burned that would still tell the fan to spin, but not ignite. What else can you tell me?.

Thom

---------- FOLLOW-UP ----------

QUESTION: Thom, what happens if the furnace looses power to spin the fan...I'm guessing that would close the sail switch which would turn off the gas.  If the sail switch sticks and the system continues to attempt to ignite, would that explain the burning smell?

Answer
When the fan slows, the sail switch drops and closes off the current to the gas valve and stops ignition, as a safety. Then you should not have a fuel source, so no burning smell should occur. Unless the gas valve is not shutting off completely. If the sail switch sticks, the thermostat should still tell the board to shut down. But I think it is possible for a slow spinning fan and a stuck sail switch to produce a rich burn that would smell and blacken the outside of the rig.
Be safe.

Thom