From: John De Armond
Newsgroups: rec.autos.tech
Subject: Re: AC recharge question
Date: Sat, 19 May 2001 02:51:42 -0400

BOB URZ wrote:

> You have peaked my interest on the home make recycle unit.

I described it right down there! Really not much more I can tell you
about it.

> How do you "Distill" it from the Propane tank?.

Ignoring the issues that surround contamination from R134a and the
many blends, the major issues with recycling R12 are:
non-condensable gases (air mainly), moisture and decomposition
products (chlorine, fluorine, CO, CO2 and various halogenated
hydrocarbons.)  My approach is to divide and conquer each
contaminant separately.

To get rid of moisture and noncondensables, I chill the tank of raw
Freon to -20 dig F.  At this temperature, the vapor pressure is only
0.6 psi.  If I open the tank valve, what comes out is mostly the
noncondensables, along with a little Freon vapor.  At the same time,
the moisture is mostly frozen and immobilized.  I'm lucky in that I
own a restaurant with a walk-in freezer kept at -20 but if I didn't,
I'd probably use a bath of dry ice and alcohol or even build a
cylinder chillier from an old refrigerator condensing unit.

I then warm the tank with a hot plate until I get an indicated
pressure of about 5 pi which indicates an internal temperature of
about -10 deg F.  This 5 psi head is enough to drive the rest of the
process while keeping the temperature low enough to both keep the
water frozen and the water vapor pressure practically negligible.

I hook my recovery compressor to the cold tank.  The outlet of the
compressor goes to a small condenser and then to a large liquid line
burnout filter/dryer.  These dryers are capable of both absorbing a
huge amount of water and absorbing any acid vapor that might be
carried over.  From the dryer, the liquid is conducted to another
tank.

The process is simple.  Simply fire off the compressor and keep heat
applied to the tank to keep the pressure around 5 psi.  I stop
before all the raw Fresno is exhausted so as not to have any of the
"bottoms" carried over.

I check the distilled Fresno for vapor pressure, acidity and if I'm
doing a large lot I have a sample GC'd which shows me all
contaminants.

I normally only work on equipment that I own so I don't have any
worry about contamination from 134a or the blends.  I use R406a in
some equipment but it is clearly labeled and separate recovery tanks
are used. R406a is completely miscible with R12 and the mix works
the same as 12 so even if some gets mixed in, nothing to worry
about.  On the rare occasion that I do work on someone else's
equipment, I recover to a separate tank that I can have GC'd for
contamination before recycling.  Camp stove propane tanks are handy
for recovering a couple of pounds of refrigerant at a time.  Simply
buy a cheap propane torch, cut off the torch head and drill out the
tank spud and silver solder a flare fitting to where the torch head
was chopped off.  Viola!  Instant recovery tank adapter.

> Neon John wrote:
>
> > Dave Martel wrote:
> >
> > > You should have a recovery rig so you won't waste R12 but that is
> > trivially easy to make.  You're required to have a certified unit
> > (THANKS, MACS!!) but for your own use, a homemade unit will work
> > fine.  Mine consists of the hermetic compressor from an old
> > refrigerator equipped with refrigeration fittings and a tank (a 20
> > lb propane tank equipped with a POL to flare adapter.)  The
> > compressor is normally free from an appliance repair place and the
> > propane tank can be had for as little as $20 from Wally*World.
> > Another $10 gets you the adapter fittings from Ace Hardware.  This
> > same rig can be used to distill contaminated R12 to clean it up for
> > reuse.