GoodMan Furnace GMS80904BNA Flame Problem

laff20December 5, 2012

Furnace flame ignites till blower starts and goes off in 10 seconds 15 seconds and will ignite again and will repeat all night long or until thermostat reaches temp.. System does not lock out.
No troubleshooting codes.

Started with a bad Pressure switch (no flame at that time) did receive codes for this replaced and got flame.

What I have done so far:

Replaced mother board twice.
Cleaned flame sensor.
Cleaned evaporator coils.
Verified Thermostat
Had 2 technicians who apparently have no clue.

Any help would be appreciated.

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mike_home

Perhaps the flame sensor needs to be replaced. It is an inexpensive part and should be easy to replace.

    Bookmark   December 5, 2012 at 4:01PM
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laff20

Thanks. The flame sensor was replaced. We checked all voltages coming off the board and found 14.6 (s/b 24 volts) volts coming from the 2nd (new) board relay to the gas valve. Apparently 2 boards rec'd were bad. Trying strike 3 on Mon. Will post results

    Bookmark   December 7, 2012 at 9:47PM
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mike_home

If the third board also has a voltage problem, then I suspect the problem may be the transformer. Measure the voltage of the transformer output with the board disconnected. If it is not 24 volts, then you have a supply problem. If the voltage drops after attaching the board, then it may be a bad connector or the transformer can't supply the required current at 24 volts.

    Bookmark   December 8, 2012 at 10:30AM
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harlemhvacguy

Do you have a ground wire hooked up on the line voltage supply? These furnaces will not run well without a good ground. It requires a ground to sense flame and to maintain proper voltage from transformer.

    Bookmark   December 8, 2012 at 10:38AM
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harlemhvacguy

Do you have a ground wire hooked up on the line voltage supply? These furnaces will not run well without a good ground. It requires a ground to sense flame and to maintain proper voltage from transformer.

    Bookmark   December 8, 2012 at 10:39AM
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laff20

OK here is now the latest.Another tech came out today and troubleshot the unit again.

Apparently the Pressure switch is good, but, during the stage of fire it receives 24 volts and it opens and the voltage drops out to 0 volts for a split second and cuts the flame during the start up.. Then back to 24vRepeats and repeats.

Took a known bad pressure switch and connected. This did show the correct troubleshooting code on the board.

My head hurts.

Any help again would be appreciated.

    Bookmark   December 13, 2012 at 7:52PM
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mike_home

Is this the third control board? Is the new board an exact replacement for the manufacturer's equipment or a generic version?

Are you monitoring the output of the transformer while the furnace is starting up? Is the voltage dropping below 24 volts?

    Bookmark   December 14, 2012 at 8:48AM
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laff20

OK check this out.

5th technician in and fixed finally. There was a voltage drop at the pressure switch to 0 volts for a split second, if you blinked you would miss it on the meter. Apparently I was blinking and so were the other 4 guys. The drop and raise back to 24v was so fast that it did not get picked up at the control module. There's one for the books.
Got another new pressure switch and now it works like new.I do know that every person that looked at it said the board had to be replaced including the Goodman rep.

If you guys have any questions about this feel free to ask.

I want to thank all that offered help and have a warm Merry Christmas. I can now.

    Bookmark   December 15, 2012 at 8:04AM
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mike_home

Are you saying the new pressure switch was giving a momentary false reading which confused the control board?

    Bookmark   December 15, 2012 at 10:08AM
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laff20

yes for a split second

    Bookmark   December 15, 2012 at 10:14AM
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rickb1958

ok this pressure switch problem is this a commen problem, i put a new one on and furnace worked fine over the weekend and my wife turned ac on last night and now the furnace wont light. it tries but fails and shows a gas fault. any thoughts

    Bookmark   October 6, 2014 at 8:27AM
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