Gas Furnace / AC unit fan works. Heat/AC do not
Asked May 24, 2007, 05:24 PM
This winter the furnace control board in my Lennox Gas Furnace / AC unit failed and I had it replaced by a contractor. The contractor mis-wired the thermostat inputs to the board. He wired the Green (fan) wire to the C (compressor connection) board input and the C wire to the Green (fan) board input. He properly wired the other end of the C (compressor connection wire to the yellow (A/C) input.
In this configuration the gas heat worked properly all winter (I was then unaware of the mis-wiring). But once I switch the thermostat to A/C, my problems began. At this point the 3 amp break on the board opened and everything went dead (as it should). So I found the mis-wiring issue and re-wired the inputs correctly, then I reset the 3 amp breaker on the board.
Now... the only thing that works is the fan on "on" mode. When I put the fan in auto and try to run the Heat or the A/C... nothing happens. The board LEDs show the flashes for "normal operation" but I can't get either the A/C or the Heat to start up now...
Are there any other fuses or breakers on a furnace/AC unit like this that I should be checking? Is the Board failing even though the LED show everything should be running OK? Did running 24V down both sides of the compressor do something that would prevent both the furnace and A/C from now working? Thanks in advance for any help you can provide.