Furnace pressure switches are safety devices found near a gas forced-air furnace's draft inducer motor. Its function is to keep the furnace from starting unless the proper venting air pressure is present. It's made to detect the negative pressure formed by the draft inducer motor during furnace startup and turn off the furnace if the air pressure isn't sufficient to remove the exhaust gases. Moreover, a diaphragm is attached to the switch. The diaphragm is then attached to a switch that indicates whether it is open or closed. With the vacuum’s presence, the diaphragm extends and closes the switch. However, the switch remains open if there is no vacuum. In this instance, the furnace is turned off. (2)