Suburban furnace problem

[Cougarman]

Hello. I am new to this forum and this is my first question. I have a 2015 Cougar 26dbhwe. It has a Suburban SF30 furnace that quit lighting. The fans turn on but then turn off after it doesn't light. I pulled out the unit and everything seems ok. Then I noticed that one of the two blue wires was loose from inside the wall and just pulled out. I looked at the thermostat and there is just one blue wire. Why are there two at the furnace?

[ChuckS]

The single Blue wire at thermostat is the (-) furnace signal lead to the control box mounted up in the ceiling..

The Suburban uses two blue wires. Plus and minus signal to turn energize control module , run fan, etc

In your case you need to locate where the plus side of signal wire for furnace went to before pulling our the furnace.

Your issue .. fan runs but no heat could be several things but a multi meter will narrow down issue.. Looking at it will do nothing

Remove sail switch and ohm out the two contacts while moving paddle on sail switch...must show open one way with paddle and full continuity with paddle arm moved other direction

You are looking for a reading of less than 1 ohm for continuity side...

When furnace fan was running did you listen for tell tale indication of igniter firing at exhaust.. if it was firing then sail switch is not your issue

If it wasn’t firing then either sail switch is bad, loose connections at furnace igniter module or bad igniter module

[ChuckS]

Wire diagram for Suburban SF series furnace. Should be all you need to diagnose

[dutchmensport]

Sail Switch Video, click here

. This may help.

[Cougarman]

I think the problem with my furnace is the broken blue wire. I can run new wires from the thermostat to the furnace , but I don't have access to the control box and I don't know how to determine where in the wall the wire broke. It looks like it had been rubbing on something since the trailer was built. I bench tested the furnace and everything worked.