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It sounds like you have a bad pressure switch. I recommend you replace the pressure switch on your unit.
Please hit ACCEPT so I can be paid for my time. Thank you very much!
Tell me more as I'm not following your logic. Both pressure swithes look to me to be operating ok. What I mean by this is that the switches are both closed as result of the vacuum applied by exhaust and when I remove the hose temporarily when I get the error codes... allowing both switches to open temporarily and then close again... this action gets the unit running until the next cycle. I come to this conclusion by montioring continuity in the circuit during the cycle. So the pressure swithes hold themselves closed. Why do you think the switches are bad?
Also.. why is the exhaust fan running constantly? Since my manual intervention of removing the hose seems to fix the problem, I was guessing that the furnace is supposed to be doing this itself automatically by cycling the exhaust on and off.
Hello, the issue is a stuck inducer relayon the inducer control board. This in turn is what is holding pressure switch making furnace code fault.
You are correct. The issue is now with the 2 stage control board.
It is not uncommon for a domino effect to take out the sister board like that.
For you r convenience I am including the service manual for you. Page 4 will show the 2 stage control board location.
Thank you for your patience.
Thanks Billy. I also found the service manuals earlier in the week... very handy. I have just two more questions for you as long as I've got your attention:
1. Do you have a recommended source for parts.. one you like more than others?
2. As long as I'm ordering parts, any other preventive maintenance items you would suggest replacing as well?
Thanks again for your help.
I like this outfit for parts -
As far as other preventive items, this unit really has no "routine" maintenance parts to change. I would change the board, clean blower compartment, remove vent pipe and shop vac unit out, and make sure of fresh filter.