Many high-efficiency air conditioning and heat pump systems use air handlers with two-speed fan motors. Two-speed fan motors contain a set of windings with three wire taps: common, high-speed and low-speed. When the fan runs in high speed the electricity runs across the entire set of windings from the high-speed tap to the common tap. The low-speed wire tap connects to the windings between the high-speed tap and the common. An air handler's fan motor needs a run capacitor to maintain a constant speed. Rewiring a two-speed fan motor involves connecting the motor's wires to a capacitor and a fan relay.
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Things you need
- Needle-nose pliers
- Screwdriver set
Disconnect the electricity to the air handler at its circuit breaker. The correct circuit breaker uses a "furnace" or "air handler" identification tag.
Inspect the fan motor's wire identification chart, found on the fan motor's case. The chart gives each wire's colour and its function.
Inspect the air handler's wiring diagram, usually found on the inside of the air handler's lid. The key on the side of the wiring diagram lists each part and gives the part's identification code. Find the fan relay on the wiring diagram and determine the fan relay's high- and low-speed pin numbers.
Push the terminal connectors on the fan motor's capacitor wires, usually brown-coloured, onto the capacitor's interchangeable terminals with needle-nose pliers. The capacitor looks like a metal cylinder with two wire terminals protruding from its top. The capacitor mounts to the side of the blower housing. The motor powers the squirrel cage in the blower housing.
Remove the green-coloured screw on the blower housing with the correct screwdriver, usually a 1/4-inch hex-head screwdriver. Slip the fan motor's green-coloured wire's terminal connector onto the screw. Replace the screw.
Route the fan motor's wires into the air handler's electrical connection box. The electrical connection box, usually located at the top of the air handler, contains the air handler's electrical control parts.
Push the terminal connector on the fan motor's common wire, usually white-coloured, onto the air handler's common terminal block. The wires from the circuit breaker enter the air handler and connect to a terminal block. The air handler's wiring diagram identifies the common side of the terminal block, usually "L2."
Push the terminal connector on the fan motor's high-speed wire, usually black-coloured, onto the fan relay's high-speed pin, often labelled "5," with the needle-nose pliers. The fan relay looks like a black box with five or six pins. The labels, usually numbers, printed on the relay next to each pin identify its respective pin.
Push the terminal connector on the fan motor's low-speed wire, usually red-coloured, onto the fan relay's low-speed pin, often labelled "2," with the needle-nose pliers.
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