Re: Suburban furnace troubleshooting help

Yes sail switch MUST CLOSE in order for DC Voltage to go to circuit board

No DC thru sail switch then no DC Voltage to gas valve/spark electrode

Sail switch makes up when fan motor reaches 75% RPM.....dirty switch, dirty 'paddle' etc ----sail switch doesn't make up

Check for 12V DC at sail switch....both sides
Black wire to ground (DC to sail switch)
Red wire to Ground (DC from sail switch going to circuit board WHEN switch is closed)

YELLOW wire is ground source