On 2011-08-04, Snag wrote:
I know it's kinda OT but ...

My son called last night to say his central AC wasn't cooling . Went over
early this am and found that the fuse had seriously overheated , to the
point that the contact has lost tension and no longer grips the tab on the
fuse carrier (he's calling a 'lectrician today to replace it with a breaker
panel) . I rewired the AC over to the stove fuse , and neither the
compressor or fan will come on . Meter checks tell me that when he turns it
to "cool" the relay engages , and there's power to the motors - 247V
unloaded , drops to 230+- when the relay closes .
I suspect that due to poor contacts , the voltage drop at the unit has
burned up both the fan and compressor motors ... anybody out there with
experience in the field that can shed more light on this ?
I considered that maybe the capacitor has gone bad , but I'm not sure ,
and that wouldn't(shouldn't ?) cause the overheating problem in the fuse box
.

Actually -- it could. Based on when my compressor cap went bad,
what happens is that the motor tries to start, but keeps drawing current
until the overheat switch in the compressor opens. It recloses after a
certain number of minutes (IIRC, it was about ten minutes or so.) I
don't know how long it took to reach that point, but after everything
was hot, it took about 15-20 seconds for the overheat switch to open
each time. The lights dimmed each time it came on, and brightened when
it opened again, which says a lot of current was being drawn.

This is a lot more current -- and for a lot longer -- than the
normal starting surge. So it will heat the fuse clips enough to
eventually cook off the fuse itself.

Replace the cap -- note that it is a *run* cap, not a starting
cap. A starting cap will blow up very quickly in this service.

Mine had two caps in a single package -- something like 45 uF
for the compressor cap, and 15 uF for the fan cap. It happened to open
at the common ground, so I missed it when trying to measure it in place
by disconnecting only one side at a time.

We're having record high temps here , and I surely don't have room for him
and his two roomies at my house , since the eldest and his spawn have moved
back in .

Of course -- air conditioners don't fail (or don't get noticed
to fail) when the temperature is other than record high. I've been
there too many times.

Good Luck,
DoN.

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