Furnace Troubleshooting Help
Yesterday, our furnace (Ruud Silhouette) stopped working properly. I've been trying to diagnose the problem and can use some advice.
It's not freezing here (but is raining...), so I'm willing to do some troubleshooting prior to sucking it up and calling a furnace repair guy. The big challenge is that the furnace is not easily accessible - It's in a 24" crawlspace in the center of the house with access from the outside - each visit is a trip into the rain, through a 18"x20" scuttle and then a 30' GI Joe crawl. Accessing the control board, etc. is very difficult. So before I pull things (e.g. transformer, circuit board, igniter) out to test, I'd like to have some idea where I'm going.
Symptoms: both main blower and draft inducer blower run whenever there is power to the furnace. No flame. If the furnace power is cut and then turned on, both blowers start up simultaneously.
Proper start (heater) sequence is:
a) heat call from thermostat
b) inducer draft blower starts and runs for 30 seconds
c) igniter warms up for 30 seconds
d) gas - main burner on
e) main blower on
Checked thermostat, works ok.
However, no 24v on "red" thermostat wire - the power wire from the furnace controller
and no 24v at the controller output on the furnace.
Circuit board getting power and indicating "OK" via an LED, whatever that's worth.
Haven't checked igniter.
The lack of 24v suggests xformer problem, but there's power to the circuit board. Any ideas?