Here is manual that should help.
ManualI would blow the furnace compartment out good with compressed air, compressor or can will work.
Have you tested the thermostat? At furnace connect the two blue wires on terminal block. Furnace fan should start immediately. In 15-20 seconds burner should kick in. separating the two blue wires the furnace should go into cool down mode and then shut off.
If no operation, Check the circuit breaker to insure it is energized. This is mounted on motor housing.
Bud
USAF Retired
Pace Arrow
2003 Chev Ice Road Tracker