I am going through error code 31 diagnostics one by one, because that's what is flashing on the board (just installed brand new). My igniter does not work (just installed brand new), still 5 volts are at my igniter. If my inducer and pressure switch is working, then what else is left to check according to code 31? Many things in the list are related to inducer and switch. So, the only thing left is "Inadequate combustion air supply" . What does this mean and how do I check it?

Anything else I need to check. Trying to fix the problem several days. Thank you very much.

Do you have 24 volts on either side of pressure switch?

No, I checked one contact and ground then another contact and ground. Reading was 2 or 3 volts.
I removed the switch with its tube. I placed Ohmmeter on two contacts -circuit is open no sound. Once I sucked on the tube circuit got closed and I can hear beeping. It means that switch closes during negative pressure.
I still don not understand. Is switch bad or something else is going on?

If you do not have 24 volts to either side of the pressure switch then it does not matter if it pulls in or not. There must be a limit, or flame role out that is keeping the power from going to the switch.

Thank you very much
My furnace has 3 rollout switches: two at the bottom (left and right) and one at the top .
All of them have continuity (closed) with power or without. But left and right switches measure 24VAC during operation. The top one shows only 2 volts.
Is it possible that top switch is faulty and it prevents 24 Volts to be at the pressure switch contacts?

If a switch is faulty or needs reswet it will still have 24 volts on 1 side. You may have another switch in the blower compartment or some where that you are not seeing it. But you should always get 24 on one side not coming threw to the other. This meens the switch is bad or not reset