RV Repair: RV Furnace, pilot flame, thermostat switch

Question
I have an 1981 23' Prowler, the furnace is a Coleman Presidential 4319a 729. A couple of weeks ago the pilot started going out during the night, as time went by it got worse going out on every cycle. This past weekend the the heater quit working. The pilot will light but will not stay on after I release the pilot knob. I tried adjusting the pilot and it will adjust but has no affect on the pilot staying lit. The schematic I have is no help really, it tells me it has a limit, sail and thermostat switch and a thermostat but has no placement in the schematic (simple drawing they called a schematic). It seems as though all gas flow stops when I release the knob. I am not sure what to test and how to test it at this point. I am an electronics technician and have a background in elctrical mechanical but in this case the only two switches I can see look to be thermo switches and since I am working with LP I do not want to experiment. When we bought the trailer the furnace did not work, I pulled it out and removed tons of dirt dobber nests and cleaned the unit, it has worked fine for two months until now.

Answer
Gerald,

If the pilot lights but will not stay lit when you release the knob then either the thermocouple is bad or the gas valve itself is bad.  You can test the thermocouple with a volt meter that reads in milli-volts.  You will need to unscrew the thermocouple from the gas valve and apply the negative lead of the meter to ground on the furnace or the tube of the thermocouple and the positive lead of the meter to the tip of the thermocouple that you unscrewed from the valve. Next you will need to light the pilot (make sure the tip of the thermocouple is in the pilot flame) and watch the output reading on the meter. The output should be 15-30 milli-volts.  If its less than 15 it may not be strong enough to hold the gas valve open.  If it tests good then the gas valve will need to be replaced and parts for your furnace are becoming quite rare.  If it is bad you may want to consider replacing the entire furnace.