"H. R. Bob Hofmann" bravely wrote to "All" (18 Nov 04 20:57:38)
--- on the heady topic of " AC defrost"

HRBH From: (H. R. Bob Hofmann)

HRBH Sam Goldwasser wrote in message
HRBH ... "Asimov"
HRBH writes:
Hi,

I was troubleshooting my sister's donated old Viking window AC which
she said wouldn't cool a couple summers ago. Found the defrost
interruptor contact was open with traces of smoke on the case. I
jumpered it and noticed the compressor seemed to be binding at every
other start attempt. When it wouldn't start it tripped my powerbar's
breaker so that explains why the defrost contact burned. The 25uF
starting cap seems okay. It measures alright and low leakage. After a
few careful starts the compressor now runs every time.

I've heard of AC compressors locking up if not used for a very long
time. I'm guessing the oil drains out of the bearings. It seems it
will run fine from here on and it really cools fast. I'll just have to
be careful about starting it next summer and use the powerbar with
breaker.

I have a couple of question's about the defrost contact. Is it simply
a fail-safe device or is it needed to turn off the compressor as part
of normal operation? Are these pretty generic?

This one clips onto the cold end return and made by Klixon (Made in
USA) # 20425F21-439-780 F56-3.0 6CV Not too sure about the F56-3.0 as
it was smudged. It was held in place by a thick tape ressembling
mastic, some kind of thermal insulation?

None of my ACs have such a sensor so I doubt it's needed to prevent
damage to anything.

HRBH Maybe it is a sensor to shut the airconditioner down in case the
HRBH temperature gets too cold and there is danger of too much frost/ice on
HRBH the cooling coils, or maybe a shutoff if the compressor temperature
HRBH gets too high. You don't say where this sensor is located, as far as
HRBH I can tell.


It is not the compressor overheat interruptor contact. There already
is one attached to the compressor body right inside its wiring box.
The defrost interrupter contact clips onto the the pipe bringing the
cold coolant into the room radiator.

A*s*i*m*o*v

.... A fail-safe circuit will destroy others.