1979 airstream furnace will not work

[driftways]

I'm new to this form

I have just purchased a 1979 23 ft Airstream

The suburban furnace is not working. two thermostats on for ac and one for heat. I have propane, the gas cook stove works. No fan at furnace, burner will not light, the gas is on to the furnace, all fuses are good, no power at the thermostats.

Any suggestions Chip

[BayouBiker]

There is a switch and breaker on the furnace. check it for 12V power and continuity. Then the voltage goes to the thermostat and if it calls for heat, continuity returns to the furnace and voltage is present at a thermal limit switch. Also the controller board gets power from the breaker. If the thermal switch is good, the controller sees continuity through the thermostat and thermal switch and should pull in the blower motor relay. Your furnace is not getting even this far. So check these items first. Do you have a multimeter?

[GCinSC2]

Chip,

Knowing what the model number is can help select correct info from this library of service manuals https://myrvworks.com/manuals/ select Furnace and Suburban to see titles.

Also Darren has several YouTube videos for Suburbans but not sure if any apply to your model.

Do you have a mulit-meter?

Gary

G'morning Brian. Raining all week here.

[CBWELL]

Some of the older thermostats have a Off/On switch on the bottom of the housing. Make sure that it is moved to the "On" position. Also check below the furnace to make sure the valve on the gas supply line is open. This valve is on the outside of the trailer normally.

[BayouBiker]

Rain here all week too. Hard freeze expected Monday, just in time for Mardi Gras. Good thing my furnace is working, hope driftways gets his sorted.

[Belegedhel]

I would start by troubleshooting your 12V system, as described above...but if that is the original furnace, your best course of action might be to skip the troubleshooting and just replace it. 50 year old furnaces tend to have burnt/rusted through on the inside, and the users tend to wake up dead of CO poisoning.

good luck!

[Wazbro]

Originally Posted by Belegedhel

I would start by troubleshooting your 12V system, as described above...but if that is the original furnace, your best course of action might be to skip the troubleshooting and just replace it. 50 year old furnaces tend to have burnt/rusted through on the inside, and the users tend to wake up dead of CO poisoning.

good luck!

X2. If original could be blessing it didn't start.

[driftways]

Originally Posted by BayouBiker

There is a switch and breaker on the furnace. check it for 12V power and continuity. Then the voltage goes to the thermostat and if it calls for heat, continuity returns to the furnace and voltage is present at a thermal limit switch. Also the controller board gets power from the breaker. If the thermal switch is good, the controller sees continuity through the thermostat and thermal switch and should pull in the blower motor relay. Your furnace is not getting even this far. So check these items first. Do you have a multimeter?

Thank You! very helpful! I have a multimeter. I will look for the switch and breaker on the furnace

[driftways]

Originally Posted by Belegedhel

I would start by troubleshooting your 12V system, as described above...but if that is the original furnace, your best course of action might be to skip the troubleshooting and just replace it. 50 year old furnaces tend to have burnt/rusted through on the inside, and the users tend to wake up dead of CO poisoning.

good luck!

Good point and advice thanks

[driftways]

Thanks everyone, very helpful

[lemley]

Step on. Install a CO alarm.

The furnace works as follows:

Thermostat clicks on (calls for heat)
After about 5 seconds the fan on the furnace starts.
If the sail switch closes (indicating the fan is moving air) then
After about 20 seconds the gas valve opens (a soft but audible click) and the igniter begins firing. If you look at just the right angle through the sight glass you can see the electrode fire. You do have to pull the front cover off to see this.

If the flame lights it is sensed by the thermocouple (mounted with the igniter) and the furnace runs until the thermostat clicks off. At that point the gas shuts off and the fan continues to run for a couple of minutes to cool down the combustion chamber.

If the flame does not light the gas valve closes and the fan runs until turned off at the thermostat.


So.. after all of that..
If the fan never runs the gas valve will never open and you will never have a flame (you do NOT want a flame without the fan). Access the furnace and find the power wires. Check for 12 volts.

If you have 12 volts, disconnect the thermostat wires and connect the two thermostat wires coming from the furnace together. The fan should start within 5 seconds. If it does not, pull the furnace. You’ll either want to replace it or work on it from a bench.

[88Limited]

You should have 12v+ on one leg of the thermostat, on my '88 that leg was coming from the 12v+ to the furnace. So if you don't have 12v+ to your thermostat, chances are you don't have it to your furnace.

As others have said I'd start at the 12v fuse panel and make sure you have 12v going to your furnace.