Refrigeration fans can be separated into five important characteristics.
Anytime you are replacing the fan blade, you must keep them in mind.
What are they?
2. Shaft Size
3. Number Of Blades
The shaft size and rotation do not affect the actual performance.
However, the diameter, number of blades, and pitch make a difference.
It's obvious that the greater the diameter of the blade, the more air movement.
The same applies to the number of blades and pitch.
So, when do problems crop up?
If the blade is the OEM ( original equipment manufacturer ) replacement, no problem.
But increasing the diameter, number of blades, and/or pitch, watch out!
Anytime you change any of these three, you directly affect the performance of the motor.
How do you know if the new blade will work?
Snap that amp meter onto a motor lead.
If the amperage exceeds the listed RLA of the motor while running, you may have a problem.
May have a problem?
It is possible to exceed the RLA within limits.
The rule of thumb I use is 10%.
If the motor is rated for 4.8 amps, chances are it will be OK up to 5.28 amps.
However, do yourself and the refrigeration equipment a favor.
Whenever possible, replace the blade with OEM specifications.
That's the proper cfm the factory engineered the condensing unit or air handler to obtain.
One more piece of information.
I know that the topic is fans, but here's another common mistake.
Don't forget the motor's rpm rating!
Of course it goes without saying, the higher the rpm, the greater the load on the motor.
I once had a complaint that a condensing unit continually tripped the high pressure control.
What did I find?
The prior technician had installed the wrong rpm motor.
The higher rpm caused the motor to run higher amps, overheat, and stop, tripping the control.
Guess he figured the higher the rpm, the more air!
The more air, the lower the pressure!
Refrigeration is great.
It loves to stand logic on its head!
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