If Pressure Switch is Good,
Then Some Probable Causes for the Pressure Switch turning off are:
- Inducer Motor Blower Wheel Stuck, Seized or motor is Bad.
- Inducer Motor Slowing Down because of age.
- Lack of 120 volts to Inducer Motor.
- Limit on Inducer is Triped or Bad (If it has one).
- Short in wiring (less likely).
- Defective Control Board.
- Bad Start capacitor on Inducer Motor (if it has one).
- Flue Vent Restrictions.
- High wind outside.
- Blocked or Cracked Pressure Switch Tubing.
- Inadequate Combustion Air.
- Cracked Heat Exchanger.
- Improper Vent Size, or Improper Vent Pitch.
Click on the picture to see Flowchart and Testing Tip
How to Test to see if a Pressure Switch is good:
With the furnace inducer motor starting up, place meter probe of your volt meter on the lead wire going to the switch and the other volt meter probe to ground (on a 2 wire switch). You should be reading 24-28 volts. Next check the switch hose(s) for cracks, leaks or blockage. Next check that the switch is open (on most models) while the furnace is off.