Furnace Inducer Motor: Testing, Noises and When It's Really the Pressure Switch

On any modern gas furnace, nothing happens until the inducer starts and the pressure switch closes. That makes the inducer one of the first things to check on a no-heat call.

Safety: A failed inducer or blocked vent can push flue gas into the home. Never run a furnace with the inducer disconnected or the pressure switch jumped. Check CO and draft after any repair.

How it fits into the sequence

1. Thermostat calls for heat.
2. The board checks that the pressure switch is open (not stuck closed).
3. The inducer starts.
4. The pressure switch closes once the inducer pulls enough suction.
5. The igniter warms up, the gas valve opens, and the burners light.

If the pressure switch doesn't close within the board's time limit, the furnace stops and usually flashes a code. See how to read furnace flash codes.

Step by step

1. Read the LED code before cycling power.
2. Call for heat and listen. Does the inducer start?
3. If it doesn't start: measure line voltage at the inducer plug while the board is calling for it.
   • No voltage: the board isn't sending it. Check whether the board saw the pressure switch already closed (a stuck switch stops the sequence), then the board's inducer relay.
   • Voltage present, no run: turn power off and spin the wheel by hand. If it's seized or tight, the inducer is bad. If it spins freely, check the motor's windings for an open circuit.
4. If it runs but the furnace doesn't light: the pressure switch isn't closing. Measure the suction at the switch with a manometer and compare it with the switch's rating (printed on the switch). Then check:
   • The hose for cracks, kinks or water
   • The switch port and the inducer tap for blockages
   • The vent for blockage, too much length or too many elbows, or a sag holding water
   • On 90%+ furnaces, the condensate trap and drain See pressure switch troubleshooting.
5. If the suction is low with a clear vent and hose, the inducer may be weak: a dirty or damaged wheel, a failing motor turning slowly, or a leaking housing gasket.

Noises and what they mean

Replacing an inducer

• Use the exact replacement listed for the furnace model, or a kit the manufacturer approves. Inducers are matched to the furnace's venting and pressure switch.
• Replace the gasket with the new inducer, and seal it as the instructions say.
• Check the pressure switch hose and the switch while you're there.
• Run several cycles and confirm the pressure switch closes reliably, then test CO and draft.

Common mistakes

• Replacing the inducer when the pressure switch hose is cracked or full of water.
• Replacing the pressure switch when the vent or trap is blocked, so the switch never sees enough suction.
• Jumping the pressure switch to "test" the furnace. Never do this with the burners firing.
• Ignoring a noisy inducer in fall. They tend to fail on the first cold night.
• Not checking the vent after the repair. A new inducer can't fix a blocked flue.

FAQ

Sources

• Goodman 80% Single-Stage Furnace Service and Troubleshooting (RS6621301)
• Rheem R96V Installation Instructions (92-24161-124)