Sorry for this not being properly crossposted, I meant to but forgot
to add this news group to it when I put it on rec.autos.tech
A lot of folks here in home repair know AC systems so I thought there
might be some good ideas here.
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Twice now my 92 Explorer has "blown" the compressor. In both cases
it blew very shortly, within minutes, of starting the truck. It blew
so shortly after starting the truck I have a hard time seeing how the
pressure could be high enough to "blow" but in both cases it popped
the high pressure relief valve and spewed oil and refrigerant out. The
first time it did it I had started the truck, pulled out onto the
street and immediately hit a red light. While at the light I put it
in neutral and gave it enough gas to rev up the engine to 1500 rpm to
run the compressor enough to get more cooling in the 100 degree heat.
After less then a minute of waiting at the light there was a
grunge/screech/smoke/smell and no more cooling. Seemed like the
compressor had locked, oil blew, fan belt screeched over the locked
pulley and the oil burned on the exhaust manifold. Then it unlocked
but no more cooling. Upon tearing it down there was the expected
"black death" look to the oil, it had about 100K miles on the system,
and metal bits at the orifice tube screen. When I took the compressor
apart there were broken bits and obvious new wear marks on the
internals. I got a new compressor, accumulator, orifice tube and
condenser and flushed the evap and all lines. Put it back together
and it ran fine for 4 years.

Then last month I started it up after it sat all day, about a 95
degree day. Started it and just let it idle for no more then 1 to 2
minutes while I arranged my stuff before leaving. Then
grunge/screech/smoke/smell and no more cooling - same thing again but
I hadn't even sped up the engine. Immediately turned it off. Got
out and looked, oil blown out all over the engine again. Turned it
back on and the compressor spun freely, no funny noises, but no
cooling. Unlike the first time, when I tore it down I didn't find
anything much in the system, no little metal chunks, just a little bit
of "blackness" to the oil, a small amount of sludge on the O-tube
screen. The inside of the compressor did not seem to have any broken
parts. From how everything looked I might have been able to fix it
by simply recharging it but I had already ripped the compressor apart.
So I bought all new parts again and redid it last week. Got a
compressor, accumulator, o-tube and condenser from rockauto for $220.
Now it's cooling fine.

Then about 3 days after fixing it I was at the SAME park where it had
blown the second time. Started it up and heard what I thought sounded
like the grudge noise - like the fan belt was just starting to slip
and was fighting it. After having heard this twice before I
immediately turned it off. Thought maybe, just maybe I smelled a tiny
bit of burning oil but there was no smoke like the first two times.
Drove about 3 miles to the store with the AC off and a frown on my
face. Popped the hood and disconnected the compressor. Then started
the engine and turned the ac on. Then plugged the compressor back in
while I watched under the hood. Compressor came on, no funny noises,
and it started to cool!! In fact, it seemed to be working perfectly
normally. So I presume I caught it JUST in time before it blew out
the high pressure blow-off again and spewed oil everywhere.

So at this point my thinking was that maybe I was putting too much oil
in the system and slugging the compressor on start up. So I pulled
the one week old compressor back off and checked the oil level. It
was actually on the low side, certainly not at all overfilled. So put
it back together and it's working just fine.

Sorry for the long post, ...

why is this system blowing up within 1 or 2 minutes after a "cold"
start???? It's always in the 1 or 2 minutes when I would think the
system isn't even working hard yet.

Every time I start the engine (and AC) now I have my finger ready on
the AC on-off button ready to shut it off if I hear the slightest
funny noise.

I put in 80% of the amount of R12 as I'm using 134a. Running it in
the driveway at 2000 rpm I've seen the low side drop to 30 and the
high side go to over 325. I don't see how they could possibly go even
that high, much less to the 400 psi needed to pop the high pressure
valve within 2 minutes after starting with the engine at or near idle
speed.

Anyone got any theories? Too much oil? Too much refrigerant? Not
enough virgins being sacrificed?