Weird Furnace Problem

Old 11-26-05, 04:26 PM
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Weird Furnace Problem

I submitted a post a couple days ago about a problem I was having with my furnace. My furnace was
shutting off before it reached the set thermostat temperature and would have problems re-starting.
Last night I was testing some parts with a volt meter. I had the front panel off that covers the
burners, gas valve, inducer motor, and pressure switch. When I have the panel off, the problems
my furnace has been having, for the most part, go away. Does anyone know why? Below is a copy
of my original post. Thanks.

.Im having a problem with my furnace. It is a Bryant Induced-Combustion furnace. The furnace has been shutting off before reaching the set temp. The draft inducer motor seems to run the whole time the furnace is working. When the draft inducer motor stops thats when the burner flame goes out. After the burners shut off, the main blower still goes for about 1 or 2 minutes before shutting off. As soon as the main blower shuts off the draft inducer motor starts again, the pilot will light, and then the burners will light but after a few seconds the draft inducer motor stops again and the burner flame goes out. This process repeats itself over and over. It seems like the problem has something to do with the Draft Inducer motor. When the furnace shuts off before the thermostat setting is reached it is the Draft Inducer motor that is shutting off first, then the burners go out. The only way I can get the furnace to work for any extended period of time (15-20 minutes)is by shutting off the main power switch on the side of the furnace and keep it off for about 10-15 minutes and then turn it back on. The furnace will light fine and work for about 15-20 minutes but still never getting above 63 degrees. (Its been about 16-20 degrees outside the last couple of days.) Does anyone have any ideas why my furnace wont say lit and why it has problems re-lighting? Thanks
Old 11-26-05, 04:48 PM
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Stange Problem

The only thing I can think of off the top of my head which could cause this is an automatic reset limit switch. Maybe by keeping the door off enough air is getting to the switch to keep it cool. Like you said, it is a strange problem.
Old 11-26-05, 05:25 PM
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Do you have open combustion by chance? (has just one pvc pipe connected to draft inducer motor, rather than a second pvc pipe leading to the top of a closed combustion chamber).

To have a ventor shut down BEFORE the flame goes out is something I cannot recall out of the top of my head. I could theorize that for some unknown reason, especially in light of posters claim that furnace runs with the door off, which is most strange, that somehow the draft inducer relay switch loses it's contact.

If the furnace lost 24 volts, instead, let's say, that would also kill off the gas valve simultaneously, so that cant' be it. Hmmmmm. So far, I like the realy theory, but.......

I could theorize that the draft inducer should NOT shut off first, but if this was my furnace, I would run the furnace with the door off, and then, one test at a time, unplug safety switch wires and pressure switch vacuum tubes to see just what shuts off first.

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