A furnace pressure switch detects the venting pressures within a heating and ventilation system and is not adjustable to different pressure levels. The switch prevents the operation of the furnace if the appropriate venting pressures are not present.
A single stage conventional furnace uses a pressure switch with a single hose connection, while a single stage condensing furnace uses a switch with two hose connections. Some furnaces, such as two-stage or modulating, may have more than one switch.
The pressure switch detects the normal drop in pressure generated by the combustion blower between the burner box and the inlet side of the combustion blower. The switch closes to complete the electrical circuit when a preset level of negative differential pressure is present.