How to Fix Furnace Problems With a Stuck Pressure Switch

The pressure switch on a furnace detects when the blower motor is running. Among other features, the switch prevents cold air from blowing through the ductwork until the burner or electric element reaches a temperature sufficient to produce warm air and the heat exchanger is at the proper pressure to circulate the air. The device operates on air pressure, which closes a plunger in the mechanism, activating the switch. The plunger slides in and out on a tight-fitting tube. If the pressure switch is stuck, the plunger is typically the problem. Try fixing minor problems before replacing the switch.

Nut driver set
Pliers
Silicon-based spray lubricant
Screwdriver set
Replacement switch

Instructions

- 1
  Shut off the furnace at the circuit breaker.
- 2
  Remove the bolts holding the service cover to the side of the furnace, using the nut driver. The pressure switch is located near the top. A clear plastic tube connects from the switch to a nozzle on the blower assembly.
- 3
  Pull off the tube at both ends and blow through it to verify there are no clogs. Reconnect the tube.
- 4
  Spray a short burst of lubricant on the switch plunger and slide the part back and forth, using pliers if necessary to loosen the switch.
- 5
  Reconnect the hose and turn on the furnace to test. If the switch plunger does not activate, shut off the furnace at the circuit breaker and continue troubleshooting.
- 6
  Remove the two mounting screws holding the switch to the inside of the furnace. Pull off the hose and the two wires attached to the switch terminals to remove the part. The wires slip off with Y-shaped connectors on the ends.
- 7
  Mount the new switch in place and secure with screws. Slide on the two wires to their corresponding terminals on the new switch and push the end of the hose onto the switch nozzle.
- 8
  Replace the service cover with the bolts and nut driver.
- 9
  Turn on the furnace at the circuit breaker.

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