What happens when a pressure switch goes bad and how to check it?

TY

When a pressure switch is not closing the furnace will not fire. Many times the switch itself is not the issue, but a restricted vent, plugged condensate drain, weak inducer motor, etc, etc is the culprit. You can check the pressure switch a several ways. Most common ways to test is to check for voltage from each terminal to ground (should be 24v at each terminal when draft inducer is running) or to unhook both wires and check for continuity across the switch terminals when draft inducer is running. However, as I said, if the switch is not being pulled closed, I would start by checking drain system, vent and intake air pipe (if applicable) and also make sure draft inducer is running. Lot of option here, but these are the basics. Please let me know what your furnace is doing, and what you find.