Multi-speed blower motors are standard on almost all modern HVAC air handlers. Changing the speed of the air handler to a slower setting can reduce allergens and alter the interior humidity level in the home, which can be beneficial in the winter when the heat is being used. Switching the air speed can be accomplished easily with a few simple tools.
Disconnect the Power
Locate the air handler electrical disconnect box and disconnect the power. Following the wires from the air handler until they reach a metal or plastic box housed near the unit. Once that box is located, open the disconnect box and flip the switch to the "OFF" position. To be extra cautious, the buss bar can also be removed.
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Locate the Blower Motor and Wiring
Using a nut driver, unscrew the air handler cover. The 1/4-inch and 5/16-inch nut drivers are the two most common sizes for the nuts securing covers. Remove the cover from the air handler. Locate the fan motor and inspect the wires that are coming from it. There will be two wires on the air handler's blower housing that will lead to the capacitor. The rest of the wires will lead to the electrical control box. On the other end, one wire will go to the terminal block labeled "Neutral" or "Line 2," and a wire going to the fan relay will control fan speed.
Identify the Speed Wires
The remaining wires, generally capped off with wire nuts, are speed wires. Locate the identification tag for the fan motor, which will be somewhere on the fan or motor block. The tag will identify each of the speed wires by the color of their wire insulation. As each manufacturer uses their own color coding system, it is imperative to verify each wire correctly. With this information, it is possible to identify the current fan speed. A manual can be found online if you no longer have the HVAC owner manual.
Change the Active Speed Wire
Locate the fan relay electrical terminal and remove the current fan speed wire (normally "high") from it. Cut the wire's terminal connector off with wire cutters. Secure the old speed wire by twisting a wire nut over the end. Locate the wire for the new speed setting ("medium" or "low"), remove the wire nut from its end and use wire strippers to strip 1/2-inch of insulation from the end of the wire. Slip the speed wire into the round end of the connector. Using pliers, squeeze the stripped portion of the speed wire to the wire terminal connector. Secure the rectangular end of the electrical connector to the fan relay on the electrical terminal.
Test the HVAC System
Close the air handler's cover and secure it with the removed screws. Turn the power on and test the air handler's fan. You should be able to hear a difference from the former speed. At the end of the season, you can switch the speed back to high for the summer months.
Air speed switches have become the standard on modern HVAC systems. That's largely due to the fact that being able to switch fan speeds on the air handler allows for a greater seasonal energy efficiency ratio (SEER), saving homeowners money on electrical costs.