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My American Standard furnace (“Standard” Model, year 2003, 12 or 13 SEER) gave an Error Code 2 when first turned on- “External lockout, retries or recycles exceeded.” (4 fail to ignite cycles observed.) I turned off the switch for maybe 30 seconds and turned it back on. It ignited in the second cycle, heated the house, and shut off. When it came back on later, it was not blowing hot air. No flame, Error Code 3- “Pressure Switch Error.” This has happened several times.

The pressure switch reads open at rest. If I use a straw to suck on the tube, there is a reading of about 3.9, trending down to about 3.2 before I have to stop to exhale. I think this rules out a bad switch. The inducer motor runs, and the fins on its fan appear to be clean. There don’t seem to be any obstructions in the air flow, but I can’t take the vent sections apart, as they are snapped firmly together. I went up on the roof, and the vent was clear. If I turn on the furnace and let it run without igniting, should I be able to feel a definite air flow when I go back up on the roof, or a suction on the tube from the inducer motor? And is it a bad idea to jump the 2 pressure switch wires to mimic a closed circuit? I want to rule out everything else before I try to replace the circuit board.