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!