Goodman furnance Air pressure switch – faulty

There are a couple of things that it might be: It could be the flame sensor. I have seen them where they look clean but are dirty enough that the DC voltage being generated is not enough for the circuit board to keep the gas valve open. I would pull it out and clean it with some scotch brite or a brillow pad. be care full not to damage the porcelain base. It is generally fairly easy to remove, one or maybe two 1/4 screws holding it in place. Gently pull it out and clean it with the pad like you would if you where sanding a wooden dowel. The 2nd thing it might be (less likely) could be a roll out switch. If your air filter is dirty it would prevent enough air flow across the heat exchanger to keep it from over heating causing the roll out safety switch to open. If this is neglected for a long period of time it can cause the ROS to weaken and begin to trip at lower than designed temperature. ps. there are typically LED lights on a the circuit board that will blink error codes to help in diagnostics. It is best to capture that info and will usually point you in the right direction.

You have a bad high limit switch, or the furnace is overheated. The high limit switch is in place to make sure the furnace doesn't heat up to the point that it damages itself, or anything around it. If the furnace gets too hot, the limit switch opens. When the switch opens the burners turn off, but the blower continues to run in an attempt to clear the heat. Once the heat is removed, the limit switch should reset (if it's an automatic reset type). In the case of a bad switch, it never resets, so the burners never come on.

Limit switches can go bad with age, but more often than not fail due to overuse. Dirty filters, blocked return ducts, closed registers, really anything that restricts air flow through the system can cause the furnace to overheat. If this happens too often, the limit switch will die prematurely.

Have a local licensed HVAC technician install a new limit switch.