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How-to: Selecting the Correct Condenser Fan Blade

Posted by Craig Bagdon on

When replacing a condenser fan motor, it’s always advised to replace the condenser fan blade along with it. Here’s the reason why – condenser fan motors commonly fail when their bearings fail. The motor’s bearings often fail when the fan blade the motor is driving isn’t balanced properly. By replacing the condenser fan blade when you replace your condenser fan motor, you can rest assure that the fan blade is balanced properly and will rotate in a perfect circle.

Replacing a condenser fan blade is fairly straightforward. The four items that you’re going to need to take into consideration are the direction of airflow, the diameter of the fan blade, the motor’s HP and the motor’s RPM rating. By using these four items, you can have confidence in knowing that your selected the proper replacement condenser fan blade for your new condenser fan motor.

Determining the direction of airflow.

When moving air with a fan blade, you either push it forward or your pull it back over the motor. To push air forward, you need to match the rotation of the fan blade with the rotation of the fan motor. A CW motor paired with a CW fan blade will push air forward – as will a CCW motor paired with a CCW fan blade. To pull air back over the motor, you select the opposite rotation on the fan blade to the rotation of the fan motor. A CCW motor pair with a CW fan blade will pull air backwards – as will a CW motor paired with a CCW fan blade. It’s important to note that shaft rotations are given from shaft end orientation.

Measuring the radius of your fan blade.

The next step is measure the radius of your existing condenser fan blade. While fan blades are rated by diameter, best practice is to measure the radius by starting at the center of the condenser fan blade and measuring out to the outer tip. Simply take the radius and multiply it by two to give you the diameter.

Finding the motor’s HP and RPM rating.

To find the HP and RPM rating of your new motor, simply look at the motor’s nameplate specifications. Almost all motors have this information printed onto a sticker that’s attached to the side of the motor.

Putting it all together.

To put all of these things together and select the right fan blade – you’re going to use Lau’s chart on propeller performance of heavy duty condenser fan blades. First, find the section of the chart that has your diameter. Next, turn your motor’s fractional HP into a decimal and match it with the proper RPM without going over the listed HP (see example below). Finally, select the proper rotation based on your desired direction of airflow. Click the part number and you’re done.

Don’t forget the interchangable hub!

EXAMPLE: You have a 1/10 HP motor with an 825 RPM rating and you’re looking for an 18” diameter condenser fan blade. Turn 1/10 HP into a decimal to get 0.10 HP. Browse the 18” diameter fan blades and look at the HP ratings for 825 RPM. Notice that the 23 degree pitch blade is rated for 0.103YOU’RE Your 0.10 HP motor comes in right under the 0.103 HP, so this would be the proper replacement blade for a 1/10 HP motor at 825 RPM.
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