How can I determine if the pressure switch is faulty on my Rheem Criterion II Furnace?

Take the two wires off the pressure switch and connect them together, now try to get the furnace to run. If is does this will tell you that there is a problem in that area. It could be a bad switch, or it could be a reset button has popped out and needs to be reset, or it could mean that the rubber hose has a leak in it.

So if it does work connect the wires back where they belong and look for anouther cause for the trouble.

I have a rheem 90 plus and what the cause a pressure switch to fail