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?
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.
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.
On 27 Mar 2006 15:01:53 -0800, email@example.com wrote:
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.
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
having no luck finding one.
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.
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.
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
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
I had thought about replacing the handler
(it's also quite noisy) and it's a reasonable
P.S. Find me a decent HVAC technician who
will work for $50/hour and I'll hire him.
On 28 Mar 2006 07:58:02 -0800, firstname.lastname@example.org wrote:
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.
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