Two part reply:
IF it started out fine then suddenly only cold air odds are low battery...
However: What is the outside temp? Sometimes moisture (Water) gets in the lines and freezes, when it freezes i the regulator thigns do not work, this is easy to test though.. Cook dinner on the stove (or heat water with propane) if these functions work,, not a frozen regulator
Butane has a vapor temp of around the freezing point of water,, Propane is closer to -40,, Some dealers, epically in the south, sell the lower cost Butane as Propane. To test.. Same as above, if the stove works, and the water heater,, NOT your problem.
part 2: This is a boiler plate, I put it together the hard way (Fixing my Furnace).
When the T-Stat calls for heat the control board starts the blower (1)
The blower blows closing the sail switch (2)
The control board then opens the gas valve (3) and begins sparking (4.1)
Gas Flows (5) And ignitets (4.2)
The flame heats the flame sensor (5)
The flame sensor sends .480 volts to the control board (6)
which then detects the .480 and continues operation (*)
When the T-stat says "Enough already" (RV is now warm)
The control board shuts off the gas flow (*)
and then turns off the blower after a cool down (*)
*: At nearly every step the control board is involved. IF IT IS BAD, things will not work.. I recommend replacement boards from Dinosaur boards.. When Mine went out the Dino board was less than half the price and when opened the box the quality of construction and workmanship, and then design was very clear to my trained eyes.
1: No 12 volt to furnace, blower motor shot
2: Low 12 volt, air ducts clogged, blower "obstructed" bad sail switch
3: Bad solenoid, Clogged Gas Jet
4: .1: Bad ignition circuit (high voltage) on control board. .2: Points too wide (Very common it seems)
5: These do not often fail but they can
5: Bad connection, NOTE:
5 and * Bad wire.
* applies to all steps by the way So does bad wire/connection.
