On Thursday, June 18, 2015 at 3:30:08 PM UTC-4, 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.

This story has been going on awhile now and this is the first
time I've heard that it takes lots of attempts to start. From
what we were told, it sounded like it started up OK, but after
running for a considerable period of time, it would then shut
off from the compressor overheating. That is different than a
hard to start issue. So, which is it?


So, he
installed a 'kick starter' kit, and it started right up (coincidence?),
and began to cool the house.

I thought it always started right up.


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.

Well, there you go.....

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 don't remember the long story here anymore, but I think the fan
was replaced recently? Sounds like he's saying that they put in
a 1075 fan instead of 825. If so, that's not good. If it has the
same HP rating as the old fan, but it's trying to run faster, then
it will overheat and could shutoff.



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.

You're right. He's only looking at part of the equation. He's right
that at the faster speed, it will move more air. But the power required
goes up at the cube of the speed. So that fan motor would need to be
~2x the hp of the original, or 1/2 hp.



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.

I told you a week ago to take a 6 pack out with a chair, sit by the
unit, and see if the fan quits first, then the compressor over heats
and quits. That would indicate a fan problem, which from everything
else you've said so far, appears to be what you had. First fan probably
was bad and they replaced it with a faster one that also quits because
it's the wrong one.