Pressure Switch
Proves the inducer is venting the furnace.
Furnace Blowing Cold Air: A Diagnostic Order That Finds It Fast
Why a gas furnace blows cold or lukewarm air, in the order to check it: thermostat fan setting, lockouts, flame proving, limits, gas supply, and duct leaks.
Furnace Inducer Motor: Testing, Noises and When It's Really the Pressure Switch
How a furnace draft inducer works, how to test one that won't start, runs noisy or runs but won't prove, and how to tell an inducer problem from a pressure switch or venting problem.
Furnace Pressure Switch Troubleshooting: Open, Stuck Closed and Dropping Out
Diagnose furnace pressure switch codes by measuring the inducer's draft with a manometer and checking vent, intake, hose, condensate trap and switch.
Furnace Short Cycling: 7 Causes and How to Pin Down Which One
Diagnose a gas furnace that lights and shuts off too soon, from flame sensing and limit trips to oversizing and thermostat settings.