Bryant 90 plus furnace burners will not light

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Old 05-04-14, 12:29 PM
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Bryant 90 plus furnace burners will not light

Re: Bryant Plus 90 Model 398AAW036080ABBA (installed in the mid-1980's)
S/N 4684A17396

The inducer assembly leaked causing condensate to accumulate and eventually found it's way into the connector to the main circuit board and shorted out the board. I replaced the housing assembly, main board, and connector.

I then turned on the unit and... The inducer motor comes on right away, then the igniter comes on and lights the pilot. A few seconds later you can hear the gas valve but the main burners don't ignite. In fact the gas valve is making noises that I never heard before. Sounds like the solenoid opening repetitively - here's a link to a short video of the sequence. Bryant Plus 90 Problem - YouTube
Maybe someone can listen and let me know if it sounds like the valve is shot??

Also read about pressure switch but don't think that's the issue. Normally closed contacts make the circuit. Bypassed the switch and same issues.

I'm thinking the gas valve got fried when the main board got short circuited?? If the recommendation is to replace the gas valve. The model number (of the gas valve) is 646AX-1 and the part number is 301273-704. I found other valves with similar numbers but none that match this exactly. a 646A-W, 646A-X, 646AX-2. Also found a 646AX-1 but a part number 301273-707. What's the difference and are they interchangeable? or is another model recommended?

Thanks!!
 
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Old 05-04-14, 03:23 PM
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Sounds like you have a bad connection or wire. Pull the wires off the gas valve and look for corrosion.
 
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Old 05-04-14, 04:52 PM
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In your video it looks like the pilot flame is faltering. If that flame isn't full and normal - the main gas valve won't open.

That furnace is over 25 years old. Have you ever had it professionally cleaned ?
That would include the heat exchanger, burner and pilot assembly.
 
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Old 05-04-14, 04:54 PM
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I pulled all wires off the vacuum switch and gas valve and re-inserted them on the connectors. No Luck!
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The gas valve is just above this - note vacuum line on bottom of valve.
 
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Old 05-04-14, 06:32 PM
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I too don't like the looks of the pilot. It shouldn't be wavering like that. A professional cleaning & inspection of the heat exchanger would be a prudent move.
 
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Old 05-04-14, 06:45 PM
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No - never had it cleaned professionally.
I just cleaned the burner area and the drain lines including the condensate trap. Pilot seemed to be working so I stayed away from it. Probably should have done the heat exchanger while i had the inducer assembly off the unit

I should have done the video with the burner box open. It's steady until the gas valve ties to open and then it seems to falter; thought it had something to do with malfunctioning gas valve??

Where are you going with the cleaning issue? If it's really blocked the pressure switch would shut down the burner? N/O and N/C contacts on pressure switch would engage. I took the wires off the pressure switch and connected the common to the N/C wire and it did the same thing.
 
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Old 05-04-14, 06:57 PM
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Any equipment that old really should be inspected. It is entirely possible there is a problem with the heat exchanger due simply to wear & tear over the years. Even if there is no problem with the heat exchanger, if it were mine, I'd be a lot more comfortable knowing things had been checked & found to be OK by a pro.
 
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