"Akka" wrote in news:1155451606.008019.324930
@h48g2000cwc.googlegroups.com:

We continue to have problems with our engine-driven refrigeration
system, and wondered if anybody knows what we might be doing wrong. We
keep on blowing up compressors -- either they start to leak after a
couple of months use, or they fail (i.e., no longer bring down the
low-side pressure to a vacuum). We know it's not from 'slugging' ice,
because we routinely monitor the state of the return line about 4 feet
from the compressor, and it's never frozen. When the compressors leak,
we naturally don't know it until the fridge doesn't cool anymore, when
we look at the sight glass and see it's empty. This entails running
the system for 5 minutes or more, empty, because that's how long it
takes for liquid to appear in the sight glass when the system is full.
Is that a long enough time to ruin the compressor? The last time we
opened the system up, we found some black residue blocking one of the
filters at the expansion valve. Any idea how dirt could have gotten
into the system? Maybe from a compressor going bad? How do you clean
it all out?



I'll make some guesses.....(c;

Make sure there is a loop in the return line from the cold plate to the
compressor for residual freon to collect in and boil off (you don't see
moving freon freezing the outside of the line).

Make sure the suction side of the cold plate is the TOP of the cold
plate, sucking freon gas off that has already boiled. I've seen a couple
hooked up upside down that blew the compressor sucking liquid.

Does it have a dryer bottle on the system to get the residual water out
of the liquid line? The bottle may have come apart inside, filling the
expansion valve with material you're seeing. When it becomes clogged,
the expansion valve opens and may pass the stuff onto the compressor
through the cold plate, jamming the compressor, but not very likely.
Replace the dryer bottle, anyway.

OK, you've put the vacuum pump on the system and sucked all the air out,
right? (I say this in jest as I met 3 who thought, wrongly, they could
just blow the air out with freon, which won't work.) How much
refridgerant OIL did you pump in before charging it?? Oh? It needs
special OIL?...(c; Yes, it does, or the compressor will lock from lack
of lubrication. Many don't know it. They just start filling it with
freon and run it dry....not good.

That's two things that make a compressor blow.....no lube oil....and the
biggest cause - pumping LIQUID freon!

The compressor's very low in the system so any liquid freon that didn't
boil off flows downhill into the cylinders made-for-gas-only. You'll
hear a knocking sound as liquid freon hits hot pistons from heat-of-
compression. The freon explodes in the hot cylinders, boiling off
immediately. The pressure the explosion creates is too instantaneous to
flow out the valves into the high pressure outlet. Make a loop in the
hose from the cold plate so that can't happen, so any liquid blown out
the cold plate runs back into the cold plate, hopefully into the TOP of
the cold plate.

Anything sound familiar? What pressures are you measuring on the
Schrader valves?