Blower Motor Failure

What's the failure mode? Do they burn out? Bearings freeze up?

Blower motors should last 10's of years IMHO.

A three-quarter-horse motor seems awfully large for a blower. Maybe you should be using a smaller, rather than larger, motor -- one that wouldn't use as much energy and therefore wouldn't get as hot.

Im no hvac pro but ive heard improper duct sizing, to small, can stress a blower. It would come under an improper install issue, duct sizing. Get someone else out but first call trane for advise. To low a voltage is bad for AC motors,

They burn out.

Hi, Is the motor has good venting? Not over heating? How did it fail? Mechanical(bearing), electrical(capacitor, burnt winding)? Doesn't seem right.

I assume the venting is adequate as this is the factory set-up. It is not the cap as this has been replaced each time the motor had been replaced (and a buddy that is an electrical engineer tested it).

Sorry, to answer the last part of the question, I think is was the windings that burnt as the shaft spins freely and the motor had that unmistakable fried wire smell.

Can you safely check the ac voltage to the motor while it's running? Is it getting at least 110 V? IF it's lower while running then it's being loaded down. Checking the amps would be useful too.

Then they must be getting too hot (unless there's a design flaw in the motor, which seems unlikely, especially since you've tried more than one model). That can be because they're overloaded, or because they're getting too high a voltage (e.g. due to power surges), or because they're not getting adequate ventilation. I doubt the first, especially since you said you upsized. When you replaced the motor, did you also replace the capacitor? You should have. I'm not familiar enough with the Trane to know about how the motor is ventilated, but upsizing the motor could have worsened the effects of any shortcomings there.

I will try this. It is a 220V system so I assume you mean getting at least 210V. But assuming the voltage is OK, would the duct sizing (too small) be a likley culprit?

I am also thinking undervoltage

Low air flow is a common cause of blower motor failure. Having talked to many motor manufacturers at seminars, all state heat is the primary cause of failure. With 240 volt system, I assume you have a heat pump.

What is making your motor run hot? If the motor does not have enough air flow to cool it, it will overheat. Primary reasons of low air flow are restrictive air filter (1" pleated or 1" washable electrostatic), dirty air filter, undersized air filter, undersized duct system, registers closed off in rooms you are not using, replacing system with larger system without increasing (replacing) duct system, undersized indoor unit, reusing indoor unit when replacing outdoor unit.

When you replaced the system, did they do a manual J load calculation, or did they use the dreaded 500 sq ft. to the ton rule? Did they measure the air flow from the system with an instrument more accurate than the hand (handometer)? Did they replace the indoor unit? Did they install a new air filter system (They can be restrictive, beware) Did they install new ornamental grilles, especially wood ones (They can be restrictive, beware). Did they put in a bigger system for any reason?

Answers to these questions can help with diagnosis.

One other thing, did anyone measure the amps on the new motor(s) when they were replaced to see if they were using more power than they were rated for?

Stretch

It was a new home but who installed the furnace and duct system? You? A buddy? The building contractor? An unliscened hvac contractor? Spend a few bucks and get your system professionally checked out and repaired properly. Bubba

Buy new 1/2hp motor, always replace ran cap. ( ~$70 )

Measure ESP. And post it here. Plus your speed settings are: Cooling - high/med/low ? Heating - high/med/low ?

A sign your ducts being undersized is the cause of your issues is the noise level you note. Its going to happen again and again till you upgrade or find the cause. The original installer is to blame if it is duct sizing. Your larger blower will likely fail sooner.

loud; much louder

There should be a resident, or nearby Mr Trane that the dealer can call out. He came with some strange and wonderful test equipment that the dealer didnt have. My 16i has a 10 year parts/labor warranty. We really used it. I experienced similar loud, not properly running problem upon installation. Took some time, but after replacing the circuit board and the motor, they found out it was the connecting cable. This is particularly important if you have a variable speed air handler/system. The blower was actually running faster than called for for the unit, in any mode of operation You can go here and post your question:

Thanks to all for your feedback. You all have been a great help. To answer or clear up some of the questions for you all, this was a new house we had bulit, so as far as the method used to determine duct size, I really have no idea. I did not install nor did a Buddy install the system. It was installed by one of the bigger HVAC contractors in the Indiaianpolis area. I have had dealings with this company before and they do not own up to the fact that there is a design porblem. All of the registers are open and we never close any of them off. I will have my electrical engineering buddy come over and test voltage and amp issues. If any of you are HVAC tech's, what questions should I ask before have have another company check out my problems? My gut tells me that it is a duct sizing issue. All of the failures have been in the winter, while in heat pump mode. The fan is always set to Auto. I have never ran the fan continuously.

Trane would be your best call and should get you the answer free of charge.

Trane will only come out with a dealer that can remedy the problem. That dealer may or may not charge him. His best bet would be to call a reputable licensed hvac contractor. Explain over the phone what has been happening and that he wants the duct work sizing addresses along with whatever else will help remedy the problem. Call until you find one that can help. Bubba

Just a guess and personal observation...

Hooked up to 110 volt circuit. (or to just 1 leg of 220 V circuit).

Had a well pump like that one time...Well Pump ran fine ... but it would have killed the motor if we hadn't "caught" the problem.