On Thursday, June 18, 2015 at 4:08:03 PM UTC-4, Uncle Monster wrote:
On Thursday, June 18, 2015 at 2:30:08 PM UTC-5, Boris wrote:
J Burns wrote in :

Googling, I quickly came up with American Standard condenser motors
that run at 825, 1075, and 1625 rpm. I believe the load a fan puts on
a motor varies as the cube of the speed. If the fan was designed for
a 1/4 hp 825 rpm motor and it has a 1/4 hp 1075 rpm motor, the load
will be more than 1/2 horsepower. Overheating!

I was up there Sunday and had another company come out for a second
opinion. The tech checked all but the fan (more later), gave it a clean
bill of health, but was there when the compressor (and fan) stopped.
He suspected that the compressor was heating up because it was old and
taking lots of attempts from the starter capacitor to get it started.
All the failed attempts, he said, would overheat the compressor. So, he
installed a 'kick starter' kit, and it started right up (coincidence?),
and began to cool the house. Not sure I buy this kick starter thing,
but I kept the old starter/relay in case. He left, but within 15
minutes, the fan and compressor stopped. I called and he came right
back. This time, he said the one thing he didn't check was the fan. He
disconnected the compressor power lead, and checked the fan. It should
have been drawing 1.7 amps, but it was drawing 2.3 amps. Also, the fan
was rated to run at 1075 rpm, not 825 rpm. He told me to get the
original company out to put in the right fan...my thoughts, exactly.
And he said I did need the kick starter thing anyway. g

I called the original company Monday morning, and they sent their 'best'
diagnostic tech out that day. I told him his company installed the
wrong fan, and he tried to say yeah, but you're getting more cooling
with a faster motor, to which I said that "it was a tug of war between
more cooling vs. more amps/heat, to which the amps/heat always wins.
Besides, here is the spec sheet, and it clearly states 1/4 hp, 825 rpm.
Let's get the right fan motor in there, and see what happens." He also
checked everything else out, and said it all looked fine, including
refrigerant pressures. He disconnected the compressor power, and
checked the the amp draw of the fan...it was 3.0. He ordered an OEM
motor, and I'm going back up this Tuesday to have them install it.

After all of this, I looked back at the work orders for both times the
original comapany came out to diagnose the problem. On the first call
back, the fan check boxes said rated 1.9, actual 2.4, with the notation
"ok". On the second call back, same tech, the fan was checked, and the
this time the rated box said 1.7, but there was no actual taken. Sloppy
all around.

I'm getting really cynical now that a good a/c tech is hard to find.

The slower motor is there for quieter operation and the slower the motor, the steeper the pitch of the fan blade. The tech should have changed the fan blade to one with a shallow pitch on the faster motor to keep the load on the motor in the proper range. It will work but the fan will just be noisier. Any competent AC tech should know that because it's easy to get the correct blade and motor combination. The standard high rpm motors are usually less expensive than the slower speed motors because more of the higher speed motors are produced. 8-)

[8~{} Uncle AC Monster

Sounds reasonable, but from a practical standpoint the simpler
and cheaper thing would be to put in the right motor. A different
fan probably isn't going to be cheap.

I think you said something here much earlier about the new fan possibly
being the wrong one and that it's the new problem. Sounds like
you had that nailed. It is amazing that a AC tech wouldn't understand
that you can't just put a faster motor of the same HP in. Even if
they don't understand the physics, you would think they would have
learned from prior bad experiences.....

Me, I got my new PSC motor. Cap should be in the mailbox. Will let
you know the results......