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Gui 11-18-2009 02:05 PM

Bryant 345MAV furnace has startup issues
This furnace is about 7 years old. It's been having issues all last winter and so far the same for this season. Here's what's happening:

About 80% of the time it works perfect. Inducer motor runs for about 20 seconds, then I hear a click and burners ignite, then about a minute later blower fan comes on. All good.

The other 20% of the time I would hear the inducer motor turn on, then after about 15 seconds but BEFORE the burners turn on (and before I hear the click) the inducer motor would slow down for about 2 or 3 seconds then resume normal speed. It's as if the power get cut off for a couple seconds (never more than that - it never actually stops spinning, just slows down). After it picks up speed again and about 30 seconds later the burners will ignite ever single time and it would complete the cycle as normal.
When this happens it always ignites the second time and I've never had to reset the furnace or turn off the main power.

The status light is not flashing but I wasn't successful in retrieving any stored codes (I have the manual).

All the posts I've read suggest cleaning the flame sensor but it doesn't appear to even reach this stage of the cycle because I don't hear the "click" trying to turn on the burners. It's as if it senses insufficient airflow and decides to shut off, then changes it's mind. But it always happens at the exact same point in the cycle.

Any suggestions?


Marty S. 11-18-2009 05:03 PM

If you have a volt meter check to see if the control board is droping power to the inducer or if there's a voltage drop. If no luck there check the amp draw of the inducer motor while it slows down. Sounds like either the board or motor is about to fail.

Gui 11-19-2009 08:58 AM

OK I'll check that, but it may take a while for me to "catch it in the act".

I just find it strange that it always happens at exactly the same point in the cycle. I would think that if it were a failing motor or board it would be less predictable.

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