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Squirrel cage fans

E

Eric in IL

Well-known Member
I just put a new motor on the fan for my furnace/A.C. unit. I forgot to check the rotation direction of the failing motor before removal.

I wired the new motor for the direction that looked right, but as usual that was the wrong direction. I need to remember to make those squirrel cages spin the direction that looks backwards to me.

Even Wikipedia has it wrong in their animated visual.
Bass ackward fan animation
 
Yes, most everyone has been fooled by what looks correct to move air. The "correct" rotation for HVAC use is so the blades "throw" the air forward for even more velocity than the wheel would normally make with straight blades

Oddly applications that need higher static pressure with less velocity like a grain bin aeration fan, match what is shown in the link you posted.
 
Well Eric you are still messed up because the fan in that animation is running the correct rotation. The blade angles shown are used in material handling fans while the typical hvac fan will have them angled the other way. However no matter the blade angle it is the discharge orientation that determines which h way it should rotate. Looking in the outlet the blades should be coming at you.
 
Butch, my fan turns as you say-blades coming at you as you look into the outlet. But my blades are angled the opposite of the animation. To look at the angle of my blades and their rotation my pea-sized brain says that baby will never pump air, but it does.

Guess I should express condolences to the folks at Wikipedia, their animation looks "right" to my brain and I guess it is right.

However, my fan looks wrong yet it is right.

I'd never make it in HVAC.
 
Another way is if You have an AMProbe meter. The WRONG way takes a lot more amps. Almost two to one difference.
 
I use an even simpler method because I do not have a tool to measure amp draw.

If the curtains are dancing on the kitchen door by the register, we're good to go. No dancing, not good to go.
 
The one that will mess with your mind is a double shaft motor with a blower wheel at each end. You have replaced the motor and it rotates the correct direction for the housing discharge, but air flow is about 1/2 what it should be, what happened ?? Answer, you accidently swapped the right / left blower wheels side for side. Now although the wheels are turning the right direction for the blower housing, the blades angle of the switched wheels are trailing the direction of rotation instead of leaning into it.

I once bought an older Steiger tractor that had screaming fast blower motor speed, but did not have much air flow through the HVAC system. I opened the HVAC box to check for clogged evaporator or heater core, but both were clean, so that was not the problem. I got to looking at the double shaft blower and noticed that both wheels were installed so the blades trailed the direction of rotation, I swapped them side for side so the blades leaned into the direction of rotation. Ah !! now we got air flow LOL.
 
Ya that will work too. Just make sure the motor passes the four second test. Used in the military. Put your hand on it and if you can keep your hand on the item for more than 10 seconds, it passes. It is about 110 degrees give or take a little.
 
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