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?

what Freon's are you using? Was it a R12 system that you converted to 134A?
Is there a high pressure switch that opens the clutch? Who's system is it?

More questions then answers right know.


"Akka" wrote in message
oups.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?

"Rick" wrote in
:

what Freon's are you using? Was it a R12 system that you converted to
134A? Is there a high pressure switch that opens the clutch? Who's
system is it?



Yes, there's another angle, too! When it's converted to R-134a, you should
see just a SPRAY of R-134a in the sight glass, NOT solid liquid with no
bubbles like R-12 was. R-134a is much more cooling so we don't fill the
system.

http://www.wikihow.com/Fix-Cars-Air-Conditioning
http://www.machinerylubrication.com/...?articleid=310
&relatedbookgroup=Lubrication
http://www.sanden.com/support/servic.../retrofit.html
http://www.everything2.com/index.pl?node_id=1674978

To sum up from everything I can read.....DON'T. If it was working great on
R-12, find R-12. Some sailors brought me back 4 cases of 16 oz cans from
the Caribbean islands for my old '73 220D's 2-cylinder system. They paid
68c/can for it! Damned stuff was made in TENNESEE...LAST YEAR! This
replacement business is a big EPA-sponsored RIPOFF...

The ozone hole over Antarctica got bigger, year-after-year, after the ban.
Another government lie, raising prices. The SUN causes the hole, stupids.

Larry and all other responders,

Thanks for all the advice. We learned a lot from it.

On the R12/R134a issue: too late. We converted from R12 to R134a years
ago, and the system was working fine with R134a for a long time -- now,
no longer. When we installed the last compressor (marked clearly
'R134a' all over it) last month, we evacuated the system and put in a
new dryer, a big accumulator, and of course, gas. The compressor comes
with oil in it, as does the gas, so we didn't add any more.

We put in enough R134a to just barely fill the sight glass -- maybe
that was too much! The expansion valves are on the original factory
settings -- 2 turns closed from fully open. There are 2 low spots
below compressor level in the low-pressure copper tubing: one where the
tube runs under the floorboards from the fridge to the engine
compartment, and one at the bottom of a full loop just before the
compressor.

When we last charged the system, we had 140 psi on the high side, and
something below atmospheric pressure on the low side, when the system
was running and the plates were cold. When we closed the valve on the
high-pressure side, we got 150 psi on the high side and a full vacuum
on the low side. That was the day before the compressor blew. Now it
doesn't draw down to a vacuum (only to about atmospheric pressure) and
doesn't hold the pressure differential at all, after shutoff. So we
figure it's blown.

We didn't hear any knocking sound before the compressor blew but of
course the engine was running at the time and the engine room is
sound-insulated from the cabin. Initially, we did see a light fast
flow of freon across the bottom of the sight glass, then nothing. We
waited 5 minutes, turned off the system, hooked up the gauges, and
discovered we had no pressure -- and a blown compressor.

We don't have a high-pressure valve. We do have an electric clutch,
but in practice it never cuts out because we never run the fridge more
than about an hour at a time, to avoid freezing the lines. We also
check fairly regularly after we've recharged the system with R134a that
we're not frosting the return lines.

So right now I'm concentrating on three possibilities: (1) we may have
overcharged the system, causing fluid to be forced through the
expansion valves and back into the compressor at startup; (2) the
expansion valves might be clogged up and the compressor starved for oil
because of the lack of a return supply; or (3) the new compressor
simply blew -- we discovered that 3 of the nuts on the compressor head
weren't fully tight. But that in itself wouldn't cause the compressor
to fail, would it?

The gunk on the valve filters certainly could have come from
incompatible gasses. We used to get the unit refilled from time to
time by 'professionals' and we're pretty sure at least one of them put
in the wrong gas. That was 2 years ago, but still ...

So, what to do? Apparently, compressors can't be repaired (though it
sure looks like one could replace the head gasket), so we have to buy a
new one. When we do, we'll open up the valves and inspect them,
replace the dryer, vacuum-pump the system, then barely fill it until we
see liquid running across the bottom of the sight glass. What else?
More oil? Lighter-weight oil because of the low operating
temperatures?

Akka wrote:
Larry and all other responders,

Thanks for all the advice. We learned a lot from it.

On the R12/R134a issue: too late. We converted from R12 to R134a years
ago, and the system was working fine with R134a for a long time -- now,
no longer. When we installed the last compressor (marked clearly
'R134a' all over it) last month, we evacuated the system and put in a
new dryer, a big accumulator, and of course, gas. The compressor comes
with oil in it, as does the gas, so we didn't add any more.

I thought when r134a came with PAG oil and POE is usually recomended
for marine use. Maybe I'm wrong ...


When we last charged the system, we had 140 psi on the high side, and
something below atmospheric pressure on the low side, when the system
was running and the plates were cold. When we closed the valve on the
high-pressure side, we got 150 psi on the high side and a full vacuum
on the low side. That was the day before the compressor blew. ...

150 pounds sounds real high to me. My system, a DC powered Tecumseh
compressor, runs at about 95 psi on the high side. This corresponds
to a temp about 20 degrees hotter than the cooling water.

On 18 Aug 2006 09:10:24 -0700, "Akka" wrote:

Larry and all other responders,

Thanks for all the advice. We learned a lot from it.

On the R12/R134a issue: too late. We converted from R12 to R134a years
ago, and the system was working fine with R134a for a long time -- now,
no longer. When we installed the last compressor (marked clearly
'R134a' all over it) last month, we evacuated the system and put in a
new dryer, a big accumulator, and of course, gas. The compressor comes
with oil in it, as does the gas, so we didn't add any more.

We put in enough R134a to just barely fill the sight glass -- maybe
that was too much! The expansion valves are on the original factory
settings -- 2 turns closed from fully open. There are 2 low spots
below compressor level in the low-pressure copper tubing: one where the
tube runs under the floorboards from the fridge to the engine
compartment, and one at the bottom of a full loop just before the
compressor.

When we last charged the system, we had 140 psi on the high side, and
something below atmospheric pressure on the low side, when the system
was running and the plates were cold. When we closed the valve on the
high-pressure side, we got 150 psi on the high side and a full vacuum
on the low side. That was the day before the compressor blew. Now it
doesn't draw down to a vacuum (only to about atmospheric pressure) and
doesn't hold the pressure differential at all, after shutoff. So we
figure it's blown.

We didn't hear any knocking sound before the compressor blew but of
course the engine was running at the time and the engine room is
sound-insulated from the cabin. Initially, we did see a light fast
flow of freon across the bottom of the sight glass, then nothing. We
waited 5 minutes, turned off the system, hooked up the gauges, and
discovered we had no pressure -- and a blown compressor.

We don't have a high-pressure valve. We do have an electric clutch,
but in practice it never cuts out because we never run the fridge more
than about an hour at a time, to avoid freezing the lines. We also
check fairly regularly after we've recharged the system with R134a that
we're not frosting the return lines.

So right now I'm concentrating on three possibilities: (1) we may have
overcharged the system, causing fluid to be forced through the
expansion valves and back into the compressor at startup; (2) the
expansion valves might be clogged up and the compressor starved for oil
because of the lack of a return supply; or (3) the new compressor
simply blew -- we discovered that 3 of the nuts on the compressor head
weren't fully tight. But that in itself wouldn't cause the compressor
to fail, would it?

The gunk on the valve filters certainly could have come from
incompatible gasses. We used to get the unit refilled from time to
time by 'professionals' and we're pretty sure at least one of them put
in the wrong gas. That was 2 years ago, but still ...

So, what to do? Apparently, compressors can't be repaired (though it
sure looks like one could replace the head gasket), so we have to buy a
new one. When we do, we'll open up the valves and inspect them,
replace the dryer, vacuum-pump the system, then barely fill it until we
see liquid running across the bottom of the sight glass. What else?
More oil? Lighter-weight oil because of the low operating
temperatures?

You don't fill to a mark - you fill to a pressure for given
temperatures. So for me: the low side looks about 60 psi low.

But what do I know?

Only this - no pressure into the compressor
means no lube oil.

Brian Whatcott Altus OK

On 18 Aug 2006 09:10:24 -0700, "Akka" wrote:

So, what to do? Apparently, compressors can't be repaired (though it
sure looks like one could replace the head gasket), so we have to buy a
new one. When we do, we'll open up the valves and inspect them,
replace the dryer, vacuum-pump the system, then barely fill it until we
see liquid running across the bottom of the sight glass. What else?
More oil? Lighter-weight oil because of the low operating
temperatures?

If you can find a good refrigeration expert in your area, I would
highly recommend that you sign him up. In the long run it will be
money well spent. There are a lot of subtle complexities to be
considered, from the size and adjustment of the expansion valve, the
amount of charge, compressor size, purging, leak detection and
protective circuitry. Without all of that working together as a
coordinated system, it will be either unreliable, inefficient or both.
I've had one system completely overhauled, and another replaced in the
last year, learning enough along the way to know it is not a job for
amateurs, even serious amateurs.

Alas, most of our problems have been caused by 'professionals' and
'experts'. I'd guess we've put at least $5000 into this system over
the last couple of years, most of it in $50/hour or more payments for
guys who claimed to be experts standing around waiting for the plates
to cool. And what we got for it in the end was a system that ran for 4
weeks before breaking. One guy put in a new high-tech gas that was, of
course, incompatible with the R134a oil already in the system. (That
cost us a bundle to put straight.) Another simply removed the
accumulator, saying that nowadays that's no longer needed (another
bundle, including paying for 2 new compressors in as many days.) That's
when we decided to take over, even if we don't know that much. How can
it possibly cost us more than the experts do?

And of course, now we've got you-all to keep us on the straight and
narrow. :-)

Rob

"Akka" wrote in news:1155917423.995950.135660
@i42g2000cwa.googlegroups.com:

We put in enough R134a to just barely fill the sight glass -- maybe
that was too much!

Absolutely too much R134a! That's what's happening. The cold plate
overflows with R134a which dumps excess liquid into the compressor. This
blows the hot compressor apart as the liquid instantly turns into high
pressure gas, boiling off inside the little cylinders.

There is a specific amount of R134a to put in every system, just enough to
make the whole cold plate cold, but not enough to dump excess into the
compuressor. You can no longer look at the sight glass and just keep
filling it like the old days.

There's your compressor blown problem.



--
There's amazing intelligence in the Universe.
You can tell because none of them ever called Earth.

"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?