Lennox G24 - Need help!

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Old 12-19-07, 07:04 PM
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Lennox G24 - Need help!

I have a Lennox G24 series furnace that stopped blowing air a week ago. I had a service company come out and tell me that the control board was bad, but that the pressure switch may also be bad. Long story....but they (a reputable local company) tried to charge me $1100 to replace the board and the pressure switch. I declined, and instead ordered the exact same control board for the unit and the exact pressure switch for a grand total of $134. I had a friend of a friend who is a certified HVAC installer put in the new board, and sure enough the diagnostic code showed a problem with the pressure switch. We turned off the unit and replaced the pressure switch.

When I started up the unit though, it now runs for about 3 seconds and shuts off with a constant simultaneous slow flash of both lights, which according to the codes means either a low flame, or normal operating condition (i can't tell). Calls for heat from the thermostat don't register and nothing happens. The A/C still works though. Can anyone please give me some ideas? My HVAC guy is stumped too. I really don't know what to do, and I'm just about out of money.

Thank you,
Vince
 
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Old 12-19-07, 07:54 PM
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Well, it seems that the slow simultaneos flashing is the code for normal operation. So it appears that it is simply not receiving the call for heat. Can anyone please offer any suggestions?
 
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Old 12-19-07, 09:31 PM
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What happens if you wire the R and W terminals together at the furnace?
 
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Old 12-20-07, 07:51 AM
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Originally Posted by MrGolf View Post
..but they (a reputable local company) tried to charge me $1100 to replace the board and the pressure switch. I declined, and instead ordered the exact same control board for the unit and the exact pressure switch for a grand total of $134.
Reputable? I'd report them.

I had a friend of a friend who is a certified HVAC installer put in the new board, and sure enough the diagnostic code showed a problem with the pressure switch. We turned off the unit and replaced the pressure switch.
Does HE even know what he is doing? Did he just put in a new pressure switch because of the furnace code saying pressure switch?, without ever bypassing the switch to see if it was the switch or rather a lack of internal pressure to make the switch work?, or other electrical issue upstream to the switch?

When I started up the unit though, it now runs for about 3 seconds and shuts off .....

3-5 seconds flame-out usually is caused by flame proving sensor being tarnished, which you can polish it up easily with steel wool or scotchbrite pad, yourself.
 
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