Re: OT--Electrical Question----SOLVED

"Mark" <shop@xxxxxxxxxxxxxxx> wrote in message
Has anyone seen a motor switch phase? Specifically, this is a blower motor
on a 10 ton A/C unit. Twice within the last 4 months, service was called
because of no heat. Upon inspection, they find that the blower is running
backwards (switched phase). Now, yes it is possible that someone has
tampered with the unit, but there is another unit next to it that has not
had any problems and nothing else in the building has changed. Any


To All

First, thanks for the responses. Now to fill in some facts that I should
have included. First, all the A/C units service separate zones. There is no
common duct work; that's why I didn't consider a back flow of air from
another unit as there would have had to been a large positive pressure in
the building. Second, and probably most important, the blowers are belt
driven "squirrel cages". Not easy to get spinning in the opposite direction
with just air flow. And, from what I was able to find out from 3 different
electricians ( over 120 years of experience, total ), these type blowers
will still flow air in the same direction even if spinning backwards, BUT at
a reduced ( < 75% ) efficiency. Also, without physically changing legs,
they say that the motor will always run in the same direction.

Long story short. Unit ran 12 years with no problem of "swapped phase".
Needed unit serviced in January. No air flow. Belt was broken, but at this
time the "tech?" says the motor is spinning the wrong way. Keep in mind that
the unit will flow air even if spinning the wrong way. Only conclusion, tech
didn't know what he was doing, so he physically swapped legs to reverse
motor. Now, no air flow again in April. Tech finds belt broken and the motor
is turning the wrong direction. He swaps legs and everything is back to what
it was for the previous 12 years before the tech came in January.

Again, thanks to all.