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Originally Posted by ryan1088

OP, did you make any head weigh on your problem? All the AAON units I have ever worked on needed the OEM motor because of the problem you are having. As someone eluded to earlier, it has something to do with the temperature rating. I have ha a couple rodeos with these things and many arguments of why a standard motor won't work.... We ended up putting an OEM motor on and is still running 5 years later.

Bingo !!!

OP, did you make any head weigh on your problem? All the AAON units I have ever worked on needed the OEM motor because of the problem you are having. As someone eluded to earlier, it has something to do with the temperature rating. I have ha a couple rodeos with these things and many arguments of why a standard motor won't work.... We ended up putting an OEM motor on and is still running 5 years later.

Originally Posted by Poodle Head Mikey

That's not why supply houses carry the cheapest motor. They make a percentage of profit on each sale and so of course would always prefer to sell the Most expensive items - not the least expensive items.

The reason supply houses carry the cheapest motors is because of all the numb-nuts who will call ten different places for A Price on every little thing and then always buy from the place with the lowest price.

They call it "keeping them honest" - but what they are actually doing is to ruin their source of supply.

PHM
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Amen brother. I worked in my families refrigeration wholesale company for 10 years doing everything from cleaning toilets to engineering refrigeration racks. I have seen people walk out, get in their trucks and drive across town for 15 cents and be pissed because I wouldn't come down on the price. And these are supposed to be professionals.

That's not why supply houses carry the cheapest motor. They make a percentage of profit on each sale and so of course would always prefer to sell the Most expensive items - not the least expensive items.

The reason supply houses carry the cheapest motors is because of all the numb-nuts who will call ten different places for A Price on every little thing and then always buy from the place with the lowest price.

They call it "keeping them honest" - but what they are actually doing is to ruin their source of supply.

PHM
------

Originally Posted by codgy

Have you checked c rating of motor? Remember supply houses generally carry the least expensive replacement, sleeve bearing or worse motor so they can sell another motor in 2 or 3 years.

Have you checked c rating of motor? Remember supply houses generally carry the least expensive replacement, sleeve bearing or worse motor so they can sell another motor in 2 or 3 years.

You might be on the right track but I think you may be running the wrong way

If the motor is not over amping - and the thermal opens - most likely the thermal is defective.

Forget about the condenser fan blade cooling the motor - it's not a factor.

Clean the condenser coil to spotless. After that; clean it again. Then run the unit until the condenser coil is dry and check the air temperature increase across it. If it is 10-12-15º - you are moving enough air through the condenser. If the air temperature difference is higher that that - with a Clean condenser coil - you are not moving enough air through the condenser.

To pick a blade out of the air, so to speak - check the Grainger catalog for blades of the correct diameter. Then pick the one with the greatest pitch which can be driven with 3/4HP. That will give you the largest air flow possible without installing a bigger motor.

PHM
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Originally Posted by rango

Hey Guys and Gals. Working on an old (35) AAON commercial unit. Condenser fan motor .75 hp as per data plate cuts out on thermal after about 45 min.
Assume bad bearings even though amp draw not changing, install new with cap. Same pattern. Motor draws 5 amps under load which is under plate specs.I'm thinking someone be fore replaced propeller with wrong one and not enough air moving over motor to cool it. Head pressures do seem to be slightly high. Wondering if using 4 blade fan vs. 3 blade and pitch difference, etc. I'm thinking I'd like to increase air flow by 50% or so. Am on the right track?
Thx
Rango

I ended up jumpng up to a 1 hp5.2 amp and it's been fine for acouple of days.Thanx all.

Sorry I didn't see what the amp rating on your current motor was? I always sized my motors to match ampeage as close as possible to unit name plate amps. OEM does strange designs on their motors to get what they are looking for, indoor blower motors are worse. Replacement motor are generic and the HP doesn't always match the the load it is working at. Also raising and lowering a fan blade inside the fan orfice will change the amount of air it moves, and you can see that in your amperage. Thats a way to fine tune a generic motor. 3, 4 or 5 blades can all work if the blade pitch is less as you go up in number of blades. LAUparts.com has a fan to HP motor chart you can download online. Sometimes I had to up an HP size to make a motor work. In 20 yrs I hardly had a problem here in Phx replacing motor/ fans.

If the fan blade originally had a three prop blade and now you have a four prop blade, that will make the amp draws go up. The Aaon RTU's I have worked on always have three prop blades.

Strange. The old motor did the same thing? What's change? How long has the unit worked before hand because if its worked for years then the fan blade isn't the issue. No play in the bearing moving the shaft up and down? Spins free? I've seen motors bad out of the box but doubt it. And it's for sure going out on thermal? I would say check voltage but you've answered that with amp draw.

Nope, 10 mf
Cap circuit only running .70 amp

Does the motor say to use ex: 5 cap with 240 volts and at 7.5 at 208?

Since Larry retired, nobody at AAON knows anything about these old units unless you have the part number,and then it's just the part.

Don't know why but when a condencer fan motor goes on a aaon your better off getting repl. directly from aaon. Had a summer when I tried everything then someone from talk straightened me out,almost a proprietary thing.

Sounds like you need a higher amp rated motor, sometimes you go with a higher hp to match amp draw of spec. motor.

Coil clean,rpm correct. Label says original motor was 6.75 amp.

original motor spec may have been for 60C motor for condenser applications. Verify clean coil. some 3/4 motors have lower amp rating than others. also is rpm correct?

Amp draw is just under plate value.
seems like more air is necessary for cooling.

Ummmm... no...lol.. what is the name plate FLA? If your close to being under then fan blade is correct. If there is not enough load a motor will over heat. Check voltage, connections, make sure the blade is in the center of the openning.

Condensor fan size/pitch question

Hey Guys and Gals. Working on an old (35) AAON commercial unit. Condenser fan motor .75 hp as per data plate cuts out on thermal after about 45 min.
Assume bad bearings even though amp draw not changing, install new with cap. Same pattern. Motor draws 5 amps under load which is under plate specs.I'm thinking someone be fore replaced propeller with wrong one and not enough air moving over motor to cool it. Head pressures do seem to be slightly high. Wondering if using 4 blade fan vs. 3 blade and pitch difference, etc. I'm thinking I'd like to increase air flow by 50% or so. Am on the right track?
Thx
Rango