Furnace troubleshooting
Posted: Sun Oct 09, 2005 9:48 pm
Hi Sam,
Our 14-year-old suburban furnace has been pretty bulletproof, so my first guess is an immobile fan and second guess is a wiring short.
If the fan can't turn (frozen or blocked, say by an insect nest) that could cause a big current draw on the motor. You can look at the inlet and exhaust ports (our suburban has a vertically stacked double port and nearby single port); if that's blocked, then that is certainly a problem.
You may be able to get to the electronics without removing the unit, so that would allow measuring voltages to see if the problem is the wiring to the unit.
But to really see what's going on, you may have to remove the furnace, which isn't too hard. After disconnecting the gas and a few screws, ours slides toward the inside (the outside vents needn't be removed). That exposes one of the fans, so you can see if it turns freely. Our electrical harness was long enough to run it in the aisle without gas.
FWIW, our suburban has a single motor that drives 2 fans, one for outside air and one for inside. Once that starts, the fans blows a "sail" switch into the "on" position, which starts the furnace after a delay. If the fans don't work, the sail switch stays off, preventing gas and ignition without proper ventilation.
Our 14-year-old suburban furnace has been pretty bulletproof, so my first guess is an immobile fan and second guess is a wiring short.
If the fan can't turn (frozen or blocked, say by an insect nest) that could cause a big current draw on the motor. You can look at the inlet and exhaust ports (our suburban has a vertically stacked double port and nearby single port); if that's blocked, then that is certainly a problem.
You may be able to get to the electronics without removing the unit, so that would allow measuring voltages to see if the problem is the wiring to the unit.
But to really see what's going on, you may have to remove the furnace, which isn't too hard. After disconnecting the gas and a few screws, ours slides toward the inside (the outside vents needn't be removed). That exposes one of the fans, so you can see if it turns freely. Our electrical harness was long enough to run it in the aisle without gas.
FWIW, our suburban has a single motor that drives 2 fans, one for outside air and one for inside. Once that starts, the fans blows a "sail" switch into the "on" position, which starts the furnace after a delay. If the fans don't work, the sail switch stays off, preventing gas and ignition without proper ventilation.