Bryant downflow - constant fan cycle
Hi -
I have a Bryant 373LAV/376CAV (not sure exactly which one) mounted horizontally in the attic that is <5 years old and has been functioning perfectly since installed, including for the first few months of this winter. This morning when I woke up, I realized that the fan was in a constant ~1 minute cycle, even with the heat off. This is not the main blower fan, it's the smaller fan (maybe the fan switch?). The fan that is next to the gas manifold, not under the logic board.
The heat works perfectly when I turn the thermostat on and the temp up high enough for it to turn on:
- The smaller fan comes on for about 30 seconds
- The ignitor turns on and eventually glows brightly
- the gas turns on and all the burners light up
- the main blower comes on after about 1 minute and blows heat
- when I turn off the thermostat, the burners go out immediately, the main blower stays on for about 1 minute, then shuts down
About 3-4 seconds after the main blower fan shuts down, it starts this cycle:
- The smaller fan comes on for about 30 seconds
- The ignitor turns on and eventually glows brightly
- I can hear a relay click and the ignitor goes off
- the small fan continues to run for about 5 seconds
- the small fan shuts down for 3-4 seconds (everything is off)
- the whole process above repeats over and over: the smaller fan comes on for about 30 seconds...
There are no error codes reported (solid red led). When I power off the unit and power up, I get the normal 90 second main blower operation (and the '12' error code indicating 90 second power-on blower), followed immediately by the fan/ignitor cycle outlined above. If I turn off the gas valve, the switch on the gas valve and then power up, it runs for 90 seconds, tries to startup, and goes to a '33' error code which I assume would be caused by the gas turned off. The logic board seems to be working to me.
The strange part is that when I turn the temp up high enough, the heat kicks on and works great. But once the heat goes off, the smaller fan cycle just continues over and over.
I'm pretty handy and have no problem changing any parts if I knew where to start. Does anyone recognize this problem or have a suggestion on how to troubleshoot?
Thanks!
Mike