Very good explanation especially about the expansion valves. Except up here
in Quebec Canada we vacuum the system, then do a leak test on the system
with nitrogen we pressurize the system with about 250 psi and wait 15-30 min
with a gauge on it. If it leaks then we go around with a bottle of soapy
(Palmolive) water to check for leaks it's the law here now. There is a
actual flush compound it is pricey not sure about the mineral spirits but if
it works for you and you get good results ....

--------------------------------------------------
From: "Roger Sisler" <rogersisler2000@YAHOO.COM>
Sent: Thursday, June 19, 2008 12:54 PM
To: <vanagon@GERRY.VANAGON.COM>
Subject:      Re: AC High Side - line leak - rubber hose

> Keith, new compressors have a shelf life of 18 months and then they may
> start to leak from the shaft seal.You may need to charge in a can each
> spring. If you are switching over to 134a, it is best to get a matching
> expansion valve for 134a. Not hard to do as valves specifically for R12
> don't exist anymore-except for NOS parts(and you don't want one of these).
> A
> place called Vintage Air, in Texas, may have these R12 valves.
>
> SIDE TRACKED A BIT HERE-- The R-12  valves failed in R12 Vanagons of
> 1983.5-1985 vintage because a disk that pressed upon the actuation needle
> slipped out of place and jammed the system shut. This was a VERY  common
> period  valve that was used in many different vehicles and after market
> kits. Cars such as AMC, Ford and Lincoln are only a few. It was made by
> the
> Singer sewing machine company(Do they exist anymore?).  The installation
> of
> the Vanagon expansion valve was unique in that it was mounted sideways.
> All
> the rest were mounted conventionally, with the "head" up, and worked fine.
> During a very cold winter the R-12 in the sensing bulb and metal parts
> inside would contract beyond the parts tolerances and allow the actuating
> dish to slip sideways a 1/4 inch off center, and jam. When spring came,
> that
> was it. Some slipped and some didn't. I took apart about 5 or 6 of these
> and
> they all had the same problem. I stopped tearing them apart.
>
> Your system of 50 feet of hoses needs flushing out to change the old oil.
> 80
> percent of this needs to be removed. Ester oil is compatable with most
> newer
> refrigerants and is a good choice ( Is this related to ester-c and ester-e
> vitamins? :>)). Most of the nasty old oil is in the evaporator and does
> not
> want to come out, so you  must get all the oil from locations that are
> more
> accessible to meet the 80 percent standard. You will need to disassemble
> most of the hose connections. I use mineral spirits, a funnel,  and a
> compressor to do this, myself. Pour it in, let it sit for a few minutes,
> blow it back and forth, and then out-repeat.
>
> That vacuum pump thingie will work, but it needs to be left on for a long
> time. Lots of people leave a regular vacuum pump on overnight. I don't
> know
> how long you will need to leave that pump you have on, but it uses a
> compressor, so the compressor will need to run for along time.
>
>
> ANOTHER SIDE TRACK--- 1/20TH of 1 drop can shut an A/C system down. It
> happens this way: Moisture circulates with the refrigerant and oil. The
> dessicant bag in the dryer is supposed to attract and lock-up this
> moisture,
> but it can become overwhelmed or damaged. Free water will circulate in the
> liquid state and collect at the expansion valve where the refrigerant is
> forced, at high pressure, through a pin hole. The refrigerant temapture
> drops to below freezing at this point, and the water it contains turns to
> ice. The ice starts to collect at the opening of the expansion valve and
> eventually blocks the opening completely. The system shuts down. Water
> also
> combines with R-12 to cause serious corrosion and oil contamination. If
> this
> R-12 and water mixture is burned, it creates a Phosgene gas that is
> dangerous. This gas was used in WW-1. Be surgically clean and desert dry.
>
> After flushing out and vacuuming the system, and you are ready to
> charge-in
> the R-12, do a leak test. Let your vacuum pump stay connected, but turn it
> off. Watch the gauge for about an hour to see if you loose vacuum. Maybe
> longer than an hour. If you have a leak, tighten up on the connection a
> bit
> and retest.
>
> Change the valve cores with cores rated for a/c systems. You can get them
> at
> an a/c supply shop. Don't use cores that are for your tires. Valve cores
> are
> a major leak source. All the hoses and such are non metric. If you have an
> electronic leak finder, charge in a few ounces of refrigerant and do some
> checking before adding the enitre 48 ounces, or so.  A soapy solution for
> leak testing is very good and available a the a/c supplier. So are answers
> to questions. If you can remove the evaporator, do it. Teh box that
> contains
> this needs work  most times. There are seals that Home Depot can provide
> and
> keep the air flowing best. This way the evaporator can be dealt with best,
> too, this way. Make sure your drain tubes are well attached.
>
>
> Good luck
>