- A Furnace Draft Inducer Motor Vents Toxic Gases Outside.
- A Furnace Pressure Switch Confirms the Draft Inducer Motor is Working.
The inducer motor is a small fan that pulls air from the combustion chamber and vents it out of a home.
Since the flames in a furnace are toxic carbon monoxide, they must be vented outside.
When the inducer motor is running, it creates a small vacuum inside the furnace combustion chamber, which makes sure all toxic gases are vented.
For safety, a pressure switch is used to tell if the inducer motor has turned on. It does this by sensing the vacuum that the inducer motor creates and closes a switch.
If the inducer motor does not turn on, then the pressure switch stays open and keeps the gas off.
When an inducer motor goes bad, it will either stop spinning or get out of alignment and make noise when they spin.
The motor and the fan blade are balanced and aligned at the factory, so if you have to buy an inducer, you will likely have to buy the whole assembly.
Example Furnace Draft Inducer Motor on Amazon.
Fasco A143 3.3″ Frame Shaded Pole OEM Replacement Specific Purpose Blower with Sleeve Bearing, 1/50HP, 3000rpm, 115V, 60Hz, 0.95 amps
To test the pressure switch a multimeter needs to be used and measure the continuity of the switch as it opens and closes.
This is done by taking the two wires off the pressure switch and touching them with the multimeter leads. The multimeter should be set to read continuity.
When the furnace is turned on, the draft inducer motor will begin to blow the air out the vent and create a vacuum. The vacuum should be measured by the pressure switch, which will close the switch. A multimeter will see if there is any change and if the switch closes or not.
Example Furnace Pressure Switch On Amazon.
Furnace Vent Air Pressure Switch
Steps to Test the Furnace Pressure Switch
- The two wires on the pressure switch are disconnected.
- A multi meter is set to read continuity and the leads placed on the switch.
- The furnace is then turned on.
- If the switch is working, it will close and show on the meter.
- If it is not working, then it will not close, and the meter will not change.
If the pressure switch test bad keep in mind that the diaphragm needs to see a vacuum or it will not work.
Often when this happens something is clogging the line to the switch or stopping air from the inducer motor from being vented.