The draft inducer fan runs as long as the tubing to the pressure switch is off, but shuts down as soon as I replace the tubing or suck on it to close the switch. Does the fan or the switch need replaced?

Hard to say without being there to test the system, and Im sorry to say I have no good advice here, as this is certainly a different type of problem than the average. Does your pressure switch have two or three wires going to it? What type (make, model and serial number) of furnace to you have?

Furnace is a Concord RGU 80A100 D14. Switch has two wires and if I unhook one the inducer will run but of course the cycle doesn't go further. Usually when the inducer kicks off I get a circuit board self check error, but once in a while I get a pressure switch error code instead. Thanks for taking time to help.

What does the code say word for word. Try unhooking one wire, let the draft motor start for a couple seconds and rehook the wire. Does the furnace fire when you do this?

As soon as I rehook the wire the inducer shuts down. Codes are 'circuit board self-check failure or incorrect wiring to board' and 'pressure switch failure'. I have unclogged the port on the inducer that the tubing goes in to and checked the flue for draft.

Sure starting to sound like a board issue, but I would hate for you to replace the board and find that it wasn't the issue. I really think this may be one for an onsite tech. Please let me know what you find.

I was afraid it was the board, too, when I couldn't find the problem with a Google search. Thanks for your help.