If your furnace blower motor appears to have stopped working, try turning the fan by hand. If it works, the stop/start function of the capacitor has failed and needs to be replaced. A capacitor is similar to a battery in that it stores an electrical charge. Electrical motors that require an extra push to make them rotate use capacitors. The capacitor feeds the motor extra power until the fan starts moving at a predetermined speed, at which point the capacitor turns off. It will switch back into circuit once the furnace blower motor drops below the predetermined speed. Follow these instructions to install a furnace blower motor capacitor.
Step 1: Purchase Capacitor
Make sure you get the right capacitor for your particular furnace. Look up the make and model of your furnace to have as information when consulting hardware stores for a new capacitor. Capacitors cost about $12.
Step 2: Turn Off the Power
Start by turning off the power at the circuit breaker or by removing the electrical fuse for the circuit that powers the furnace.
Step 3: Remove Panel
Remove the metal panel on the furnace that covers the blower motor and capacitor with the screw driver. This panel is usually indicated by a tag on it saying that the blower motor is behind it.
Step 4: Built-In Power Switch
If there is a built-in power switch, it will be located inside the panel you just removed and needs to be switched off.
Step 5: Location
The capacitor will be located on the side of the blowing housing, although it may be located elsewhere in the furnace.
Step 6: Marking Wires
Take note of where the two wires connect to the old capacitor by marking them with the sharpie.
Step 7: Removing Wires
Be sure not to touch the terminals when removing the wires. Remove the wires using the needlenose pliers.
Step 8: Lifting Out Capacitor
Once the wires are removed safely and making sure not to touch the terminals, lift out the capacitor.
Step 9: Install New Capacitor
Installing a furnace blower motor capacitor is basically the reverse of removing the original one. Start by carefully inserting the new capacitor into place beside the blower motor.
Step 10: Reattach Wires
As you have them marked, it should not be difficult to relate the new capacitor to the old one and know which wires go where. Reattach the wires with the needlenose pliers.
Step 11: Return the Panel
Screw the panel back into place making sure to reattach the built in power switch if there is one.
Step 12: Test Capacitor
Turn on the power and turn on the furnace to check to make sure your new capacitor works.