Furnace fan works but no heat

[Makalu1]

First of all, yes, I checked to make sure the propane was on.

My furnace heater seems to work intermittently. When I turn the thermostat on heat, I hear an electronic click and the fan always comes on, but no heat comes out sometimes. Is my problem with a short or something with the ignition? How do I diagnose this?

Thanks!
Scott

[Ben10281]

what type of heater do you have? Suburban propane one? If so, there is a glass window that you can check to see if your igniter has actually ignited the propane and that the burner is burning or not. I would check that first. The clicking sound is the igniter sparking, but does not necessarily mean that ignition has occurred.

[N147JK]

When you call for heat you should hear the fan start up and hear one click - that's the gas solenoid opening up. Then you should hear repeated clicking as the igniter tries to light the gas. This cycle will repeat 3 times, if necessary. The fan should be running the whole time. If no heat is detected after the third try, the system will shut itself down.

In your case, what's the complete sequence of events you are experiencing?

[rallypanam]

Check the 'sail switch'. Common failure point that will prevent ignition.

[Scalf77]

Originally Posted by rallypanam

Check the 'sail switch'. Common failure point that will prevent ignition.

And before you get to the sail switch, check your battery voltage. You can try plugging in or have the van running to bring the voltage level up. The blower needs to be going a certain RPM to close sail switch (the rpm is higher as altitude goes up). Lower input voltage lower RPM, sail switch doesn't close gas valve doesn't open.

[Makalu1]

Yes, it's a Suburban NT12S. I've only opened the furnace area once before. I never knew of this window you speak of either, but I'll be looking for it momentarily. The blower fan was recently replaced after burning out from dauber bees mudding up the works.

As for the sequencing, all my ears have ever heard is this one click that seems to come from the thermostat itself, then all I hear is the fan coming on followed by heat a moment later. I don't hear these other clicks, but it works most of the time.

This is what I am seeing now. What's with the two lose wires?

[N147JK]

Originally Posted by Makalu1

What's with the two lose wires?

Someone forgot to reconnect the thermostat?

[Makalu1]

Now that I get a good look under the cover it's a wonder any air is going where it's supposed to go. Big hole in one hose (which way is the air moving?) and the other so pinched it's almost flat.. I'm guessing that "window" is that opening in the lower right or I have more cover to remove yet.

Also, what is this "sail" switch and where is it located? How does it work?

Thank you!

[Makalu1]

This looks pretty sloppy to me.

[REF]

Originally Posted by Makalu1

Also, what is this "sail" switch and where is it located? How does it work?

Thank you!

A sail switch is placed inside either an intake or exhaust pipe or tube, they have a catch “sail” connected to a switch, triggered by airflow.
A common use is inline exhaust ventilation ducting for makeup air systems.
The sail switch is placed inside of the exhaust duct and when the exhaust is turned on, the sail catches the airflow, is pushed down and the switch is triggered which is then wired to a remotely located motorized baffle that then opens allowing fresh air in.
It is possible that the hole in your hose once held a sail switch, the wires would have powered it.
I don’t believe my Suburban heater that I removed had a sail switch, but I could be wrong.