York furnance pressure switch open

[DoItMyself]

I am getting a "pressure switch open" error. In my case, the furnace ignites, but soon goes out and all I get is cold air. I have been away from the house over a year and the people responsible for taking care of it didn't and it just sat vacant with the heat on. I just moved back and found the filter was really bad and looked petrified. I replaced the filter. I have checked the hose and it seems to be clear. From what I've read, I doubt I have a bad switch. I think this is probably a cleaning problem, but I'm not sure exactly what I am supposed to clean. I do have some condensate, but I'm not sure what I need to take apart or where specifically I need to look. I really hate to pay someone to come out and clean. Any suggestions?

[HayZee518]

what does the pressure switch monitor? gas pressure or plenum air pressure? Or does it monitor air pressure in the induced exhaust air going in the chimney?

[HayZee518]

A gas pressure switch would be a totally enclosed type switch. Air flow switch would be a diapragm type or a sail type switch connected to a microswitch.