air handler motor after radiator

[semenzato]

Greetings experts,

I recently replaced a 3/4 HP motor in one of my air handlers. The older motor was starting too slowly and it blew the fuse while trying. I suppose that the capacitor might have gone bad, but it didn't occur to me to check. The motor was quite old.

Pretty much all motors I have seen on the web have a maximum operating ambient temperature of 40C and they have a thermal switch to prevent overheating. Unfortunately the dorky designer of my air handlers placed the motor in the air flow after the radiator. I searched hard and found a "farm duty" motor that tolerates 50C. It still overheats, so my air handler runs for a few minutes (10 or 15) then it stops, then it starts again after 20 minutes or so, and so on.

This is the second new motor I am trying. In the first motor (1/2 HP, the original rating), the overcurrent protection triggered before the motor could get to speed. I am getting a bit annoyed. My next step would be to disassemble the motor and short the thermal protection switch. So there. Will the motor fail too quickly? How else (short of replacing the air handler) can I fix this problem?

Thanks! Luigi Semenzato

[Joseph Meehan]

You sound like the guy who wants to take down a load bearing wall in him home without checking.

Be aware that the thermal protection device is there to keep you house from burning down, not to protect the motor.

[semenzato]

This seems somewhat doubtful. There are plenty of electric motors without thermal protection. The protection is more common in the more expensive motors, probably not because they are more likely to start a fire. I find it fairly unlikely that a burned out motor would start a house fire, particularly a motor that's not within reach of combustible material (inside a metal air handler), and on a circuit that's protected by fuses and breakers. It seems more likely that one of the rotor coils would melt and open the circuit, and the motor smells bad and is dead, period.

[Bubba]

This is a simple fix. Remove the two power wires from the motor. Remove you shoes. Stand in a puddle of water. Grab both ends of the wires and energize the power. This should fix it for everyone. No one needs a menace like you around futzing up stuff for some other poor sole to walk into. Bubba

[semenzato]

Thanks to the subtle suggestions from knowledgeable posters, I am beginning to get the sense that this may not be a good idea. Any suggestions on where I can buy a 48 mount, 3450 RPM, 120V, 1 phase,

3/4 HP motor that will work in higher than 50C ambient temperature? I am having no luck finding one.

Thanks! Luigi

[Joseph Meehan]

It's your home and your family. If you don't really care about them, that's your decision.

[Joseph Meehan]

How old is this system? I would give some thought to replacing it. You may be able to move up to a higher efficiency unit, may even get some tax breaks or a rebate.

You also might want to consider reworking the present system to put the air handler before the heat source.

[m Ransley]

If the unit was instaled backwards pay to have it redone right, cant cost more than a few motors, and you will be throwing away alot of them and wasted time messing with something you should never have started to mess with in the first place. Id take the hack to small claims that put it in backwards.

[semenzato]

This is the original system from 1969, so it's getting close to 40 years old. I don't think the unit is installed backwards. The motor pulls a belt which turns a centrifugal fan (?-looks like a squirrel cage) and I don't think that the flow through that can be reversed, neither can the handler be assembled differently.

Why should replacing a lousy motor be such a big deal? To take this to an extreme, I should hire an electrician when I need to replace a light bulb. I replaced the motor in another unit successfully, and that's why I tried this one. It was just a matter of matching the motor specs. I don't see why I shouldn't mess with this stuff. I have had a few service calls with HVAC people and they charge me in excess of $200/hour. I can buy a lot of motors and pay myself quite well (tax free too) before I get close to one of those bills, so I am not particularly concerned yet.

Unfortunately many professionals who post in groups such as this one, helpful as they are, seem to have a poisoned tooth against the do-it-yourselfers, so when they say "you shouldn't waste time with this" it's hard to say whether it's unbiased advice or just part of their attitude.

I had thought about replacing the handler (it's also quite noisy) and it's a reasonable suggestion.

Thanks!

P.S. Find me a decent HVAC technician who will work for $50/hour and I'll hire him.

[Bubba]

You can have it done cheap or you can have it done right but you CANT have both. Your post is just too damn funny. For $50/hr you'll have better luck finding a gumball salesman. Wake up man. You're living in the past. You need someone to sit you down and show you the operating expenses of keeping a heating/cooling business running. You say replacing a motor should be so easy yet you arent able to get it right. Then you curse the guy that knows how to do it correctly for what he charges? Pull your head out of the sand and wake up man. If it was so easy to do, EVERYONE would be doing it. Bubba