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Doni 05-29-2012 02:21 PM

1/4 vs 1/8 HP Condenser Fan motor
Hi all,
I got a situation, 2 family house with 2 HVACs, one is 2 Ton the other 2.5 ton
The condenser fan on the 2.5 ton unit went bad after 3 years. So I took the fan from the 2 ton unit and put it to the 2.5 ton unit. Looks to be running fine - 2nd day
However now that I want to get a new fan I noticed that originally the 2.5 ton unit had a 1/4 HP Condenser fan
While the 2 ton unit had a 1/8 HP fan.
But the coil enclosures looks exactly the same size, does the difference in Ton-size justify to put a 2-ice as powerful motor on the bigger unit? even-though the coil-enclosure seems the same size? I'm doubting the HVAC guy's original decision. Maybe that's why the fan broke? it was too powerful?

What hp size fan should I get? I don't want this thing to go bad after 3 years again

jb64 05-29-2012 03:17 PM

I have been fighting similar problems, if the motors are different, the start capacitors are probably different, I been "yelled" at here (in this forum) about the caps. I kindly recommend not to change any original design specs. look up your units on-line, or I you have the original paperwork, great! Keep everything the same, it will be one less thing to consider. If you want to "enjoy" just for fun, my condensor dilemmas threads are wires on fire, and wires on fire II. I will watch this one.

Doni 05-29-2012 03:59 PM

I'm going to double check but I think the 2 caps are the same (5mfd) even-though the motors are of different HP... go figure o_O
the other thing I was thinking was "What's so important about the more HP?" they both got the same speed 1075 rpm... but I think I get it, more horse power means it will move the same amount of air more easily ensuring the RPMs will be 1075 and not less therefore ensuring it will move same amount of air as it says, vs. a less powered motor that let's say for some reason could move less air depending on weather or rain, or etc... I'm just guessing.
But I'm sticking to what you said, just replace with same spec equipment... trust the original thinking of the HVAC guy.
Thank you all

jb64 05-29-2012 04:17 PM

not to be a pain in the :censored:, but are the fan blades the same, perhaps diameter, what about blade size, square dimensions, verticle or horizontal angle? Bigger sq. blades or a greater angle would require more energy to spin at the same rpm. On mine, they were mis-wired to start :furious::censored:

Marty S. 05-29-2012 04:28 PM

Look at the tag on the condensing unit or post a brand name and model number. Most will have the fan HP printed and those that don't usually have a FLA number. Match the FLA number to the correct speed on the new motor.

Doni 06-04-2012 09:41 PM

Marty S. You might have been on to something when you said that the fan speed should be the same. My thinking was that the new fan I got at Grainger was only 25rpms less then the original one. Not sure if that was the problem, the darn thing would heat up within 2 minutes.

Well anyhow, my problem is solved now:

I called an HVAC guy and he saw my wiring and said it looked right. But he went out and found an exact replica of my old motor, installed it and it's now up and running fine.
The lesson is, if your motor has 3 wires then find an exact replica for it, don't try to use a different one with more wires or slightly different specs. Must match the motor exactly, otherwise you're taking chances and it might not last for too long or just not work at all from the start.

I must add that my outside unit is very simple. No Starter Relay or anything like that... just the capacitor, fan, compressor.

He got the part from Source1 HVAC Service Parts.

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