York Diamond 90 - Flames out, bad board?

Old 12-19-19, 09:55 PM
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York Diamond 90 - Flames out, bad board?

I have a York Diamond 90 that began flaming out recently. With a call for heat, the ID motor will start, the pressure switch will close, the ignitor will come on, the gas valve can be heard opening and the burners will light. The furnace will then run for a variable amount of time... from a few to several minutes at a time before it will flame out. I put an ohmmeter across the pressure switch and noticed it opening up just as the burners would go out so I replaced the pressure switch. The problem persisted. I then thought it may be a flame sensor so I replaced that as well, but the problem still persists.

I pulled the 1/4 hose that runs from the pressure switch to the burner box off and noticed some strange things. For one, the heater seems to work normally, and never flames out, but I also noticed something strange happening. Sometime after the furnace lights, and is up and running, the gas valve begins to make a cyclical clicking sound and the flames inside the burner can be observed pulsing. This pulsing of the gas, will last anywhere from a few seconds to a few minutes, the flames will not go out and eventually the furnace will begin running normally again. I also noticed that during this cycling of the gas valve, if I re-attach the hose from the pressure switch to the burner box, the pressure switch will immediately open and the gas valve will close and the flames will go out. It became apparent that if the pressure switch is attached normally to the burner box, you never hear the gas valve cycling as the very first pulse opens the pressure switch and kills the flame.

I put a volt meter across the gas valve and observed that during the start cycle the voyage to the gas valve comes up to 24 volts but then when the cyclical clicking of the valve begins and the flames start pulsing, the voltage to the valve drops to between 11 and 13 volts. Eventually the voltage comes back up to 24V just as the clicking stops and the flames return to normal.

I'm thinking the 24V for the gas valve comes directly from the board... any insight, before I throw more parts money at this furnace and replace the board?


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