Coleman mobile home furnace Model #7966-756 will not turn on. The pilot light is lit, there is power coming to the step-down transformer inside the furnace. The reset switch is in the right position. It worked fine when i turned it off last spring, just wont start back up now. The blower fan will not even come on when i switch it from the auto position to the on position on the thermostat. Any ideas?

That’s a model number for a mobile home furnace. The flame sensor is inside the burner chamber. You have to turn the gas off, remove the screws that hold the two plates around the gas valve, and pull the whole burner assembly out. Be careful of the igniter, and don’t use sand paper on the flame sensor ??

There should not be a pilot on a direct vent furnace. When you turn up the thermostat for heat the 1st thing to happen is a venter motor should start, it should vent for approximately 45 seconds, the air switch will verify a vacuum in the burner box, then a spark igniter should start clicking to start the pilot, then the flame rod will verify the pilot, the igniter will stop clicking, and the main burner will ignite and remain on until the thermostat has satisfied the set point. These guideline steps must be satisfied before the controller advances to the next step. The 1st step is the venter motor running, sometimes the motor will stick over the summer months, spin it manually to unstick it. PS, nothing runs if the fan door cover is open, as that shuts down the power to the whole furnace.

Is this a blend air system? If so, there is an upper & lower control board that communicate to each other, and if the exhaust fan on the roof is out, it will give you intermittent issues. The fan mixes or blends outside air with the return of the air handler, & duals to pressurize the attic. These were installed due to mobile homes built too air tight. Without this fan, your roofing shingles will curl, and your roof decking will bow prematurely.

Heat exchanger could well be split causing it to blow out pilot

If your pilot light is lit then I would first check your thermostat. Make sure it is on heat setting and fan is on auto, turn stat up to where it should be calling for heat. If you don't get burner to light remove front cover from thermostat and see if it has a mercury switch, if it does move temperature selector up and down and see if you can see a spark in mercury switch vial. If y ou cannot see a spark remove screws that attach t-stat to base.Remove carefully and disconnect wires that go to r and w terminals on stat base. Temporarily connect these two wires together. This should make burner light if you have power to thermostat. If burner does light disconnect wires and replace thermostat. Also if you have a volt meter check across these two wires and see if you have power there. Should be around 24 volts a.c. If your thermostat has a fan on setting try that. If fan runs you know you have power to furnace The gas valve needs 24 volts to operate and inside the electric control box in furnace there is a transformer to step down 110-120 supply voltage to 24 volts. If transformer is working you should be able to hear a low buzz or humming sound. You can also check across gas valve terminals when t-stat is set for heat, you should read about 24 volts. If you have 24 volts to gas valve and it is not opening then you need to replace gas valve. The main purpose of the limit switches is to turn blower on when temperature in heat exchanger reaches fan on temp,shut off blower after burner shuts off and heat in heat exchanger reaches fan off temperature, and limit if temperature exceedes set point without blower coming on. I hope this helps you. Thanks

There is a window directly above the gas control valve. Either a spring held latch or a screw off cover need to be removed to access the pilot. To light the pilot, turn the knob to pilot and hold down while lighting pilot. The pilot in straight back inside the hole about 10 inches. Use a long fireplace match or rig a wire to hold the match. Once the pilot lights, hold the control knob down for about 30 secs., if it stays lit after release, turn to "On" and operate normally.

Go to www.grainger.com and look for a "power pile generator" this is a millivolt thermocouple that may be just what you need to make your heater work again

Is this furnace standing pilot or electronic ignition. If standing pilot i would check furnace filter then the thermastat. To test themostat first turn power off to furnace. Take thermostat off wall and take wires labled R & W and connect them together. If you have electronic ignition I would start with cleaning the flame sensor with steel wool or wire brush.If you have and more questions i will be glad to help.