Steps for replacing a condenser fan and motor on your air conditioning unit.
Most air conditioning unit or heat pumps operate with a condenser on the outside of the home to reject heat. While the units are designed to operate for 10 to 15 years, occasional repairs are required to keep the unit in good working order. One repair that a homeowner may be able to complete is replacing the condenser fan motor or blade if it gets damaged or wears out. The condenser fan is normally located at the top of the condenser covered be a circular metal wire cage. The fan has 4 props and is attached to the shaft of the motor with one or two set screws. Some older condensers have a fan mounted internally and blow air through the coil on one side. This type is typically smaller, rectangular, and shorter. Newer condensers for mini-split systems are also rectangular, but are thin and may have one or two condenser fans mounted on the side.
Removing the Fan Blade and Hub
Before you can replace the motor, the fan blade will have to be removed or a new fan blade will need to be installed at the same time. If the fan blade is in good shape, there is not need to replace it, just remount it onto the shaft of the new motor. If the hub of the fan blade very rusty and can’t be removed or the blade is damaged, you should replace the fan blade at the same time. Most fan blades can be successfully removed with out damaging it, if you are careful and properly prep the shaft. If the hub gets bent as you remove it then the fan blade will be unbalance. This will wear out the motor bearing prematurely and may cause excessive vibration. Vibrations can cause damage to other components of the condenser or crack a refrigerant line and lead to further repairs.
Look closely at the hub of the fan blade; if the blade has been replaced before then it may have detectable hub. Look for 6 screws located around the hub that hold the blade in place. These screws are usually installed with a thread-locking compound and will be difficult to remove. If the blade cannot be removed separately then a hub puller maybe required to remove the fan blade without damage. However, most fan blades can be removed without a puller by lubricating the shaft with WD-40 or similar spray and gently tapping the center of the shaft with a center punch to loosen the hub.
Clean the exposed shaft above the blade. An open mesh sand cloth works best for this to remove any rust. Rust will prevent the hub from sliding off smoothly and may damage the hub. Remove the blade set screws completely and set aside. It's a good idea to replace the setscrews if you can when you are reinstalling the blade. You should be able to locate setscrews at a local hardware store. Use penetrating oil around hub and spray directly into the setscrew openings.
Let this soak in for a few minutes before you start. If there is a keyway holding the blade in place then the blade must be pull straight off unless the keyway can be removed first. If you do not have a puller, use 2 pipes or angle iron on either side of the shaft to support the fan hub. Set the angle iron or pipes on two saw horses so that the motor hangs freely between them. Then use a center punch on the end of the shaft tap on the end of the shaft. Try knocking the keyway through the hub or just to get is move a little will help to release its grip. Do not hit the shaft directly or you will mushroom the end of the shaft and will not be able to move the blade past the end of the shaft. If the shaft end is damaged, then use a metal file on the shaft end before moving the blade.
Most condenser fan motors have a 1/2" shaft that has one or two flat spots without a keyway. After the shaft has been cleaned, place a wrench under the fan blade, near the motor and rotate it back and forth to loosen the shaft inside the fan hub. Do not grip the shaft above the blade. The wrench will leave burs that will hang up the hub. Hold the hub in one hand and let the motor hang free and the weight of the motor should start pull the shaft down through the hub. The set screws may leave a rough spot on the shaft that will hang up the hub.
Do not heat the hub with a torch. Most hubs are aluminum, which shrinks after it has been heated and cools back down. You might get the blade off, but it will not go back on to the new motor.
Selecting the Fan Motor
Over the life of your Air Conditioner you can expect to replace the condenser fan motor at least once. On the chart below you will see a list of characteristics that you need to match up for an after market Condenser fan motor. When replacing the motor, be sure to clean the shaft with sand cloth to remove any rust. Remove the blade set screws completely and set aside. It's a good idea to replace the set screws, which you should be able to locate at any hardware store. Use a good penetrating oil to loosen the blade and spray the oil in the set screw openings. Place a wrench under the fan blade, near the motor and gently try to rotate the shaft inside the fan hub. This should break the fan blade loose.
Here is the information you need when ordering a new condenser fan motor.
Size can range from 1/6 on small residential units to 1.5 horsepower on large rooftop units.
Select a motor with the same or slightly higher current draw, even if the next larger HP is required.
Service Factor (SF)
SF is the additional current draw above the rated amps the motor can safely operate without over loading the motor.
Revelations per minute the fan blade will turn at. Most use 1075 RPM. On low noise units 850 is used. You must use the same as the original motor to move the proper CFM
3 Lug Mount, Thru-bolt mount, Belly Band, wrap around mounting bracket, or Saddle/Cradle Mount for belt driven fans
Shaft Up, Shaft Horizontal, Shaft Down or Any Angle Mount. Most replacement motor can be mounted in any position.
CW, CCW, or Reversible. Most field replacement motor can be switched from CW to CCW by switching 2 wire connections.
1/2 HP and under are 1/2" with one or two flat sides - larger motors will be 5/8" shaft with a keyway
Motor shafts are 3" to 6-1/2". If the shaft is to long it can be cut to the desired length.
Most AC condenser fan motors are 5.6" or 5-5/8" diameter. Refrigeration fans can be 5" or smaller
You may also need a start-run capacitor for the new motor. Make sure you get one for your motor if the specifications are different from the old motor.
Motors can have 3, 4 or 5 wires. Make sure you get a wiring diagram from the HVAC parts distributor. The wires are usually colored black, purple, brown, orange, and yellow or white. Two wires go to the capacitor, and other 3 to the line, load and control panel. In 3-wires installations, two of the wires are connected together and not used. The wiring instructions will also tell you what 2 wires need to be switched to change the rotation of the motor.
Typical Wiring Diagram
For fans you will need to know the diameter, number of blades, pitch of the blades, and rotation. Note: You can replace a 3 blade fan with one that has 4 or 5 blades, but the CFM should be as close as possible.