Help! - I am replacing the defrost board on a Lennox 12hpb36-4p. T...

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posted: September 8th, 2008 - 2:04pm

QUESTION:
I am replacing the defrost board on a Lennox 12hpb36-4p. The old one still works but the 24v terminal strip is losing contact. The original board (68J2901) is no longer available and the replacement board (34M6301) is slightly different.
I have moved all connections to their proper designated terminals(C to C, W1 to W1, DF to DF ect.) but the new board doesn't work. Also the old boards pressure switch had (2) PS1, and (2) PS2 terminals. It was jumped from PS1 to PS2 which it shows is for PS1 only. But the new board came with jumpers attached between PS Hi to PS HI and a jumper from PS Lo to PS Lo. I tried several combinations with the new jumpers but still nothing worked. I get a blinking green light and the red light comes on for 1 to 2 seconds and goes out. I need to determine if the new board is bad. Any suggestion as to troubleshooting this board?

ANSWER: First of all don't start with thinking the board is bad there is probably a problem with the retrofit look for a failure code on the wiring diagram to tell you what the flashes mean and then call the place where you bought the board and ask for technical help but I would focus on your ps1 and ps2 issue those are pressure switch (safety ) terminals and if they are not closed that will be an automatic failure.
You could temporarily find out if this is the problem by jumping across the ps terminals and see what it does when you start it.