Check the Capacitor First (Power OFF)

Turn off power. Discharge the capacitor with an insulated screwdriver across the terminals. Pull the capacitor and test it with a multimeter set to microfarads. If the reading is more than 5% below the rated value, replace the capacitor first — a weak cap can make a good motor look bad.

Spin Test (Power OFF)

Try to spin the fan blade by hand. It should spin freely with minimal resistance. If it’s stiff, grinding, or barely moves, the bearings are shot and the motor needs replacement.

Check for Voltage at the Motor (Power ON)

With power on and thermostat calling, use a multimeter to check for 240V across the motor’s power leads (the two “line” wires). If you’re getting 240V and the motor won’t run, the motor is bad.

Check Amp Draw (Power ON — if motor runs)

If the motor runs but seems weak, use a clamp meter on one of the power leads. Compare the reading to the FLA (Full Load Amps) on the motor label. If it’s drawing significantly more than rated amps, the motor is on its way out.

Turn Off All Power

Turn off thermostat. Flip breaker. Pull outdoor disconnect. Verify with multimeter — zero volts at the contactor. Discharge the capacitor with an insulated screwdriver across the terminals.

Remove Access Panel and Photograph Everything

Remove access panel screws. Take photos of all wiring from different angles before you disconnect a single wire. Note which wire goes to Fan on the capacitor, which goes to Common (C), and which goes to the contactor.

Disconnect the Motor Wires

Disconnect the motor wires from the capacitor and contactor. Label them if needed. On most systems you’ll have 3 wires from the motor: one to the Fan terminal on the capacitor (start winding), one to the Common (C) terminal on the capacitor, and one to the contactor (run winding).

Remove the Fan Blade

Use a crescent wrench or ratchet to loosen the set screw on the fan blade hub. Sand any rust off the shaft with emery cloth until you see bare metal. Work the fan blade up off the shaft — this can be stubborn. Clean the inside of the hub with a shop towel.

Unbolt the Motor from the Lid

Remove the 4 mounting bolts holding the motor to the fan lid/grille. Most motors use a 48-frame bolt pattern (5–5/8″ spacing). The motor will drop free once the bolts are out — support it so it doesn’t hang by its wires.

Mount the New Motor

Bolt the new motor onto the lid using the same mounting hardware. The motor hangs upside down with the shaft pointing down through the lid. Hand-tighten all bolts first, then give each one only about a quarter-turn more with the ratchet.

Route and Secure the Wires

Pull the motor wires through the raceway or conduit. Use zip ties to secure wires — not tape. Keep them snug but not too tight. Make sure no wires hang where the fan blade will spin.

Install the Fan Blade

Clean any remaining rust from the shaft. Slide the fan blade onto the shaft. Position it CLOSE to the motor body — not in the middle of the shaft. This prevents air bypass. Tighten the set screw against the flat spot on the shaft. Spin the blade by hand to confirm it clears all wires and motor body.

Wire the New Motor

This is the critical step. Reference your photos from Step 2 and the wiring diagram on the new motor.

For an OEM replacement (same brand/model): Wire it exactly like the old one — same wires to same terminals. Colors should match.

For a universal motor (3-wire setup with dual run capacitor):

• The START wire (often brown) goes to the FAN terminal on the dual run capacitor
• The COMMON wire (often white) goes to the C terminal on the capacitor
• The RUN wire (often black) goes to the contactor
• The RUN and COMMON must be on OPPOSITE legs of the contactor (each on a different pole)
• If the motor has reversing leads (orange/yellow), check rotation after powering on — if air blows INTO the unit instead of OUT, swap those two leads

For a 4-wire setup (separate fan capacitor): If your universal motor requires a different capacitor size, you’ll need a separate small fan capacitor. Both LINE wires from the motor go to the contactor (one on each leg).

Restore Power and Test

Push disconnect back in, flip breaker, set thermostat to cool. Confirm: fan spins correct direction (air blowing OUT of the top of the unit), fan is up to speed, no grinding/rubbing sounds. If air blows INTO the unit, power off, swap the reversing leads (orange/yellow), and retest. Let it run for several minutes and check operation.