Front furnace

[Wambulance1949]

The FRONT FURNACE in my 2007 Tourmaster comes on for and blows cold air about 20 seconds and shuts off. ( it worked OK 2 days ago) The rear furnace works great. (FYI : The RV COMFORT.ZC thermostat was replaced about 2 years ago.) I checked the outside intake/exhaust vents and I do not see any debris or blockage. Any suggestions :?:

[Doug56]

I have found that there are micro switches on the unit that sometimes hang up. Take the outside cover off and inspect those switches.

[Wambulance1949]

I removed the cover. Put the switches through its cycles ( cool / heat) all 3- a/c's comes on ok, and only rear furnace on heat. No joy on front unit. :(

[Doug56]

I'm sorry I was not clear. The cover I was referring to is on the outside of the MH where the front furnace is located. My front furnace is on the passenger side about halfway back. I found a micro switches by the burner that has hung up not allowing the gas valve to open. The unit will shutdown in 20 seconds if it does not sense flame. You may want to check the gas valve as well if the furnace is not lighting.