Community Forums

Justin Alias · 08-01-2022, 05:32 PM

I’m replacing the original fan motor in a Carrier AirV roof unit. I purchased the replacement motor from Grainger, Item # 4UU28, and it is a near perfect match. I say near perfect because the motor body is overall shorter and it has a capacitor already built on.

I’ve attached pictures of both the OEM and replacement motors’ dataplates and wiring diagrams.

The OEM unit has a three-input, dual capacitor 12.0. The new motor has a two-input, single capacitor 5.0.

The OEM motor has four wires.
Black (High) - Coming from inside panel
Blue (Low) - Coming from inside panel
Brown (Fan) - Coming from capacitor
White (Common) - Coming from capacitor

The new motor has only three wires.
Black (High)
Red (Low)
Yellow (Line)

I know I need to make the following connections to the new motor: Black - Black and Blue - Red. However, I’m unsure as to what I need to connect to Yellow. Also, if I’m to connect to either Brown (Fan) or White (Common), then should I tap into them before they connect to the OEM capacitor?

I have the new motor installed. I just need some confirmation/guidance on the wiring before I energize it. Any help is greatly appreciated. Thank you!

Justin

MrMark52 · 08-02-2022, 06:42 AM

Yellow is the neutral aka white from the original motor going to the common terminal on the capacitor.

The brown going to the dual capacitor is no longer used. That terminal will remain unconnected on the dual cap.

Justin Alias · 08-02-2022, 12:14 PM

Thank you for your reply and the help on wiring. It was a quick and simple connect since it was already installed. Everything is working fine now. Now a nice break from the 100 degree temperatures.

MrMark52 · 08-02-2022, 01:20 PM

Thanks for reporting back!

Justin Alias · 08-10-2022, 12:09 PM

*UPDATE*

Just a week after the replacement fan motor was installed, the unit is having more issues. When I turn on the unit the fan starts fine, and much quieter than the OEM motor. However, when the compressor kicks in, it runs for about 5 minutes and blows cold air, but then it makes a clunking sound and trips the breaker. I think it is overheating because it is extremely hot to touch. The reason why I replaced the OEM fan motor is because it just stopped working. Could this have affected the compressor?

MrMark52 · 08-10-2022, 01:54 PM

Could have.

These particular compressors are designed differently than most A/C compressors. The shell of the compressor see’s hot discharge gas - as opposed to most A/C compressors that see’s cool return suction gas. So it will get hot.
They are also known as a rotory vane compressor as opposed to a reciprocating compressor.

I would be concerned with the clunking sound. But clunking could be due to electrical issues where power is intermittently making/breaking as a marginal connection heats up.

Check all the compressor wiring connections - check at the run caps, pull the electrical cover off the compressor and check the 3 wire connections there. Look at the run cap for signs of swelling. Check the connections at the PTC hard start device (I’ve had them that looked good, but as soon as I grabbed them, they fell apart in my hand).

If you have an ammeter, monitor the compressor current for the 5 minute duration. It should spike high while the compressor starts, then drop to somewhere around the indicated FLA and remain fairly steady throughout.

Not much inside a rotory compressor that can go “clunk” - and any clunking in a reciprocating compressor (which is somewhat built like a car engine) would generally prevent subsequent “cooling capable” operation.

Justin Alias · 08-10-2022, 02:49 PM

Thank your again for your reply and guidance. I'll look into everything you suggested and report back my findings.

DFord · 08-11-2022, 06:12 PM

The correct name is "scroll compressor" You can bush up on them at this site: https://www.hvacrcompressor.com/hvac...oll-compressor
Nothing goes back and forth in them. Compressing the gas is done in one continuous motion at very close tolerances.

As you've guessed, that noise a sign of major problems. Are you sure the noise is coming from the compressor? Does the fan continue to run when the noise starts?

MrMark52 · 08-11-2022, 06:25 PM

Quote:

Originally Posted by DFord

The correct name is "scroll compressor" You can bush up on them at this site: https://www.hvacrcompressor.com/hvac...oll-compressor
Nothing goes back and forth in them. Compressing the gas is done in one continuous motion at very close tolerances.

As you've guessed, that noise a sign of major problems. Are you sure the noise is coming from the compressor? Does the fan continue to run when the noise starts?

I’ve not see a scroll compressor used in a MoHo unit.

Rotary - yes. Here is an example -https://na.industrial.panasonic.com/products/hvacr-appliance-devices/air-conditioning-compressors/lineup/rotary-compressors

You are correct as to how a scroll works relative to close tolerances.

Justin Alias · 08-11-2022, 08:51 PM

No, I am not certain that the noise is coming from the compressor. I just assumed it was the compressor because it only occurs when the compressor is running. If I set the thermostat at a higher temperature to prevent the compressor from kicking in then the fan runs fine. When the noise occurs the fan does keep blowing. But shortly after, the breaker trips shutting everything off.

DFord · 08-11-2022, 09:12 PM

Quote:

Originally Posted by Justin Alias

No, I am not certain that the noise is coming from the compressor. I just assumed it was the compressor because it only occurs when the compressor is running. If I set the thermostat at a higher temperature to prevent the compressor from kicking in then the fan runs fine. When the noise occurs the fan does keep blowing. But shortly after, the breaker trips shutting everything off.

So the new fan is quieter. Are you sure it's turning the right direction? A double shaft motor could be installed either way.

You say it runs a few minutes before the noise starts. One thing is common to all compressor styles - they become liquid pumps a split second before they become junk. You can't compress a liquid.

If the fan is turning the wrong way and not blowing enough air through the coil, the refrigerant may not be boiling off completely in the evaporator. If liquid refrigerant is getting back to the compressor, I can imagine it making a lot of noise just before the liquid jams the rotor stopping it and tripping the breaker. If the problem was an electrical problem with the compressor, I doubt if it would start/run again without tripping the breaker right away.

Justin Alias · 08-11-2022, 09:21 PM

Quote:

Originally Posted by DFord

So the new fan is quieter. Are you sure it's turning the right direction? A double shaft motor could be installed either way.

You say it runs a few minutes before the noise starts. One thing is common to all compressor styles - they become liquid pumps a split second before they become junk. You can't compress a liquid.

If the fan is turning the wrong way and not blowing enough air through the coil, the refrigerant may not be boiling off completely in the evaporator. If liquid refrigerant is getting back to the compressor, I can imagine it making a lot of noise just before the liquid jams the rotor stopping it and tripping the breaker. If the problem was an electrical problem with the compressor, I doubt if it would start/run again without tripping the breaker right away.

Yes, the fan is turning the right way. Before I put the unit back together, I made sure to run a fin comb through the coil and thoroughly cleaned it with foam coil cleaner. From the sound of what you’re saying I may not waste any more time and money on an old unit. It may be more beneficial overall to just replace the entire thing.

MrMark52 · 08-12-2022, 03:30 AM

Usually difficult to put these motors in backwards because one shaft is shorter than the other.

But even if installed backwards, it wouldn’t trip the breaker the moment the compressor is told to cycle on.

You need to check all the wiring for the compressor, including the 3 wires as they connect in the inside of the compressor enclosure.

In other words, follow/complete the suggestions given in post #6.

DFord · 08-12-2022, 08:51 AM

Quote:

Originally Posted by Justin Alias

When I turn on the unit the fan starts fine, and much quieter than the OEM motor. However, when the compressor kicks in, it runs for about 5 minutes and blows cold air, but then it makes a clunking sound and trips the breaker.

Quote:

Originally Posted by MrMark52

it wouldn’t trip the breaker the moment the compressor is told to cycle on.

OP says the compressor runs for about 5 minutes before it gets noisy and trips the breaker. That's what led me to think it was liquid finding it's way back to the compressor.

(I've had many double shaft replacement motors that had equal length extra long shafts that had to be cut to length on the job.)