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Furnace Repair Troubleshooting
QUESTION:Looks like this group has allot of knowledgeable people. I am hoping that
someone could help me out on a furnace repair.
First a little background. The furnace is a Bryant +90. Model 398A
What happened last spring when the thermostat called for heat, the furnace
would intermittently run. Sometime it would compete the heat cycle other
times it would not start at all. A few weeks back I did a little
troubleshooting and found the main circuit board edge connector burnt. The
connector that plug on the board was also damaged.
I then replaced the main circuit board and wire harness. Took one lead off
at a time and installed on the new one.
When I started the furnace to see if I fixed every thing the furnace would
start normally, inducer motor would run, gas flows to the pilot and is
ignited. After a short delay appx. 20 second the main gas valve opens to
send gas to the main burners. When this happens gas stops flow- the pilot
goes out. Does this sound like the main gas valve is shorted or is there
some other thing that could cause this?
ANSWER: Does it continus cycling like this? If so, then your heat anticipater on
your t-stat may need adjustment.
If not, then what ever type of pilot proving control you have,
(sounds likea flame rod) may not be sensing the pilot and causing a lock
out. This could be caused by several things that are difficult to
trouble shoot from a keyboard. ie, low pilot, low flame signal to
control, bad flame rod or wire, grounded flame rod, bad control, bad gas
valve, etc.
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