---- Edward Maglott <emaglott3@GMAIL.COM> wrote:
> Check with local community colleges, trade schools or high schools with Tech
> programs.  They may evacuate your system for free.  They need practice for
> their students.

This might work.  In my experience in recent years the reply has always been that they only work on vehicles in a given recent age range, and that they only work on a given system (brakes, air conditioning, whatever) at a specified time in the semester in fitting with the course syllabus.  Most recently, when I asked at one local trade school, I was told that they contract with a certain large dealer in town to service the used cars, and that provides all the work the students need.

mcneely

>
> Edward
>
> On Tue, Jul 5, 2011 at 1:04 AM, John Rodgers <inua@charter.net> wrote:
>
> >  Dennis,
> >
> > No problem with the point of view. And thanks very much for all the info
> > on the what, the why and the where-for on the AC system. It goes a long
> > way in helping educate me about automotive AC systems. Something about
> > which I was totally ignorant  when I started out on this mission. My
> > goal is to educate myself about the system I am working with, and then
> > do that which I can safely do myself, and maybe hire out that which I
> > cannot.
> >
> >
> > John
> >
> > John Rodgers
> > Clayartist and Moldmaker
> > 88'GL VW Bus Driver
> > Chelsea, AL
> > Http://www.moldhaus.com
> >
> >
> > On 7/4/2011 11:22 PM, Dennis Haynes wrote:
> >
> >> I'll apologize up front for coming across a bit harsh but this question
> >> smacks of reasons refrigerants are regulated and why the EPA seems it
> >> necessary to require anyone servicing AC or refrigeration systems to have
> >> some certification.
> >>
> >> The whole concept of mechanical refrigeration relies on the "latent heat
> >> of
> >> vaporization". In other words it is the change of state from liquid to gas
> >> and back that makes this possible. In order for this work the refrigerant
> >> has to bas pure as possible. Non condensable stuff like "air" or liquids
> >> that do not vaporize like refrigeration oils all reduce the efficiency of
> >> the system. Also, any air or moisture in the system will cause internal
> >> corrosion and enough water vapor can cause ice crystals that can clog
> >> parts
> >> such as the expansion valve which can cause a blockage dead heading the
> >> compressor and causing immediate damage.   Part of charging an AC system
> >> is
> >> to pull a deep vacuum so that only pure refrigerant is in the system. Of
> >> course a new filter-dryer helps as the desiccant can deal with some
> >> moisture.
> >>
> >> As for leak testing, since atmospheric pressure is only 1 bar, (14.1 psi)
> >> a
> >> vacuum is really a poor leak test.   It will only find the big ones and AC
> >> gauges are not that responsive in the vacuum range. A properly equipped AC
> >> shop will pressurize the system with nitrogen or a dry air source say to
> >> 300
> >> psi and make sure everything holds. Then after this test is successful,
> >> the
> >> vacuum is pulled. For a system that has been open this should be allowed
> >> to
> >> go at least 4 hours or more. This will boil all the contaminants out
> >> including what is absorbed in the refrigerant oil. Stepping back if using
> >> oil from an open container, put the required amount in before the vacuum.
> >>
> >> Now the system can be charged, by weight, do not rely on pressure to
> >> determine fill, especially with R-134a. Relying on pressure will result in
> >> over fill most every time. For most Vanagons you need~1,300 grams. For
> >> R-134a you use ~85% of the amount required for R-12.
> >>
> >> Now here is where things can get ugly. As or after filling you find that
> >> you
> >> do still have a leak or you find that another part needs repair or
> >> replacement. You have no means to recover the stuff in the system. So here
> >> you let leak out or release it yourself to get rid of the pressure. The
> >> intentional release or charging a known leaking system are violations at
> >> the
> >> federal level. While individuals get away with this any regulated shop may
> >> not. You need the recovery equipment to service AC systems.
> >>
> >> Dennis
> >>
> >> -----Original Message-----
> >> From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.**com<vanagon@gerry.vanagon.com>]
> >> On Behalf Of
> >> John Rodgers
> >> Sent: Monday, July 04, 2011 5:36 PM
> >> To: vanagon@GERRY.VANAGON.COM
> >> Subject: A/C - what it the purpose of the vacuum check
> >>
> >>   What does this vacuum check do for the system in terms of servicing the
> >> A/C system.
> >>
> >> When I put my A/C system back together next week, the pressure in the
> >> system
> >> will be ambient. Is the only purpose in pulling a vacuum check to enable
> >> the
> >> refrigerant to enter the system more easily? Or a check for leaks? And do
> >> both sides of the system et checked?
> >>
> >> Thanks,
> >>
> >> John
> >>
> >> --
> >> John Rodgers
> >> Clayartist and Moldmaker
> >> 88'GL VW Bus Driver
> >> Chelsea, AL
> >> Http://www.moldhaus.com
> >>
> >>
> >>

--
David McNeely