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] 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
>
>