pressure switch stuck open

I have a high efficiency Luxaire furnance, model number: G9T08012UPB13C

About a year ago the heat went out and I had to call a repairman. They replaced the ventor capacitor (and left me with a $360 bill) and said they thought the ventor motor would need to be replaced soon.

Well a year later, the indicator is blinking 3 times again which means the pressure switch is stuck open.

This time I tried to tackle it myself. I tested the capacitor and it still has a reading of 4 mfd, which it is supposed to have. I've checked all the tubes, and gently blown into the pressure switch. I can hear the switch close when I do this. I also just detached the ventor motor - which was a task in itself. There is nothing blocking the fan blades, it spins without a problem, and in general it actually looks in really good condition. With everything clean, I reattached all the parts and tried it again. I can see the ventor motor start-up and spin freely, but I still get the 'pressure switch open indicator' flashing.

The Ventor motor part number is: 373-20717-001 Ventor Assembly

Does anyone have any ideas on my next steps? How do I tell if the pressure switch is broken even if I hear the switch close when I blow in it?

Thanks for any suggestions!

Test the pressure switch with your volt/ohm meter. An open pressure switch will have no continuity. Continuity will be present upon the switch closing. Put pressure on the tube and check for continuity.
However, I have seen an occassion where the ventor motor was spinning but not enough to "make" the pressure switch. The problem turned out to be the ventor motor not achieving enough rpm's to close the switch.