Hello all. My six year old Trane XE90 refuses to produce heat. I go to turn the unit on and nothing happens. The circuit board will blink acknowledging the call for heat, then about 5 seconds later will blink indicating a pressure switch problem (3 blinks). I took the switch off and metered acrossed the leads and physically pushed the microswitch and the switch still swithces. I have cleaned out the drain and traps. The vent tubes are clean as is the exhaust tube going through the roof. If I take the pressure switch wires and short them together will this bypass the switch so that I can see if this is the problem? I want to make sure that the pressure switch is actually bad before I buy one.