Limit/Fan & Pressure Switches.
Nordyne/Miller/Intertherm Pressure Switch (FM-632453)
A pressure switch is also referred to as a combustion air switch or a draft proving switch. The switch closes at -0.20" of WCwhen the combustion/booster motor runs creating a negative air pressure. This model replaces 632332 and 6323320. M1 Model Furnaces.