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 Control board 4544-E, Model 80UHG4/5-120A-2
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tcaimbeul

4 Posts

Posted - 12/14/2008 :  9:54:21 PM  Show Profile  Reply with Quote
Hi,
I had to change the control board a few months ago because it had burned out due to a lightning strike. The A/C mode works fine as does the blower mode but the heater is not working. Now when I give it a call for heat, the combustion air blower comes on but the ignitor is never energized off of the board. I read no voltage on J156 pin #2. It should read 120V when energized. The low voltage transformer is working and all the connectors to the board are connected properly. Checked the resistance on ignitor, 16 ohms. Can't seem to identify problem except that the board is bad. All components seem to be ok. I just hate to buy another board but that is the only thing that I can think of.
Thanks,
Tim

slctech

2086 Posts

Posted - 12/14/2008 :  10:23:23 PM  Show Profile  Reply with Quote
Sequence of operation:
1) Combustion Blower turns on
2) Pressure switch closes
3) Ignitor is energized

Check that pressure switch is properly functioning. Temporarily short terminals across switch as soon as combustion motor turns on. If ignitor then turns on then you know its a pressure issue. If ignitor is still not getting voltage from board, then it may be a board issue.
The board is designed to do a pre-check before heat sequence initiates, if the wiring is shorted before the Combustion Blower starts then an error will occur.

As a Lennox Technician I feel basic repairs and maintenance can be performed by the homeowner. But I highly suggest that periodic maintenance should be made by a certified licensed technician. You should contact your local Lennox technician for any repairs or issues that are outside your comfort zone. Property damage, personal injury, and death can occur from improperly repaired or maintained systems. Replacing a part doesn't always resolve the issue that caused the part to fail!

Edited by - slctech on 12/14/2008 10:28:13 PM
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tcaimbeul

4 Posts

Posted - 12/18/2008 :  8:02:35 PM  Show Profile  Reply with Quote
It was the pressure switch. I had jumped it previously but I jumped it before the combustion fan was activated.

Thanks for the help.

Tim
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