Electric HVAC Fan Motor Wiring Instructions

Electric HVAC fan motors wire to a capacitor and a power supply.

Most HVAC -- heating, ventilating, and air conditioning -- systems move air with capacitor-run electric motors that use two sets of wires. One wire set connects to a capacitor and the other connects to the motor's power supply, usually a fan relay or contactor. Single-speed motors use two wires to connect to the power supply. Multispeed motors need an additional wire for each speed setting. Technicians use multispeed motors to match a replacement motor's speed with the old motor's speed. Increasing the motor speed doesn't necessarily increase the system's efficiency; it often decreases its ability to change the air's temperature.

Things You'll Need

• Screwdriver set
• Plastic wire ties
• Wire cutters
• Wire connectors
• Electrical tape

Instructions

1. Disconnect the electricity to the HVAC unit. The unit's high-voltage wires usually run to a service disconnect box located within arm's reach of the unit. This box allows you to turn off the electricity to the unit without accessing its circuit breaker.

2. Open the fan motor's compartment with the correct screwdriver. Remove the top panel of an air handler, the interior air-conditioning unit. Remove the fan shroud and electrical service panel of a condensing unit, the exterior air-conditioning unit.

3. Identify the electric motor's wire colors using the motor's wiring guide. Brown wires usually run to the capacitor. Two-speed motors usually run the white wire to the power source's common terminal, the black wire to the high-speed terminal and the red wire to the low-speed terminal. Single-speed motors usually use a white wire as common and a black wire as hot.

4. Run the motor's capacitor wires to the capacitor. If the motor contains two capacitor wires, push each wire connector onto its own capacitor wire-terminal. For motors with one capacitor wire, push the wire connector onto the capacitor terminal marked "Cap." The capacitor terminal marked "COM" connects to the power supply's common terminal.

5. Run the motor's common wire to the power supply. Push the wire connector onto its common terminal. The unit's wiring diagram identifies the power source, usually a contactor or relay, and the common and hot terminals. If the unit lacks a wiring diagram, follow the wires that enter the unit to the contactor or relay and use that part's terminal identification chart.

6. Run the motor's speed wires to the fan relay. Push the wire connectors onto their respective terminals. Push the high-speed wire onto the fan relay's terminal marked "Hi" and the low-speed wire onto the relay's "Low" terminal. If the fan uses a medium speed, push the medium-speed wire onto the relay's "Med" terminal. Push a single-speed fan's "hot" wire onto the relay's "Hot" terminal. The hot terminal does not connect to any capacitor in the system.

7. Cut the wire connectors off any extra speed wires, using wire cutters. Cap the cut wires with wire connectors, then secure the connector to the wire with electrical tape.

8. Route the wires away from the fan blades and secure the wires with plastic wire ties. Pull the slack into the electrical compartment.

References

• Carrier: Wiring Diagrams
• Sub-Zero Specialists: Sub-Zero Wiring Diagrams and Schematics
• G & S Mechanical Services: Furnace and Heat Pump Fan Motors Can Be Easy to Replace and Repair

Resources

• Read this Article in Spanish
• High Performance HVAC: Condensing Units