From: John De Armond
Subject: Re: AC recharge question
Date: Thu, 17 May 2001 19:25:26 -0400
Dave Martel wrote:
> I'm leaning towards R134 myself. Cost isn't an issue, since the cost
> of changing my A/C system over to support R134 isn't that much more
> than what an A/C shop would charge for materials+labor to put in R12.
> However, R12 leaves me eternally dependent on those high-priced shops
> whereas I can work on a R134 system myself.
IMHO, changing to 134a in an older car is insane! Forget the
dump'n'pray POL oil + fittings kits. These will get you a new
compressor in short order. Doing a PROPER 134a costs serious money
as detailed here:
What is the alternative?
Stay with R12
Convert to R-406a, the best of the best alternatives.
Let's look at both options. They are essentially the same,
differing only in the cost of the refrigerant.
There is PLENTY of R12 available. Autozone (and every other car
parts place) sells R12 in blowoff cans. Yes, it's expensive. But
if you properly prepare your old system, you will buy it only once.
You need a green card but that is trivial to get. Go here:
Give them your credit card number, take the online open book test
and for $20 you have your green card that is good forever.
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
If you open the system, you'll need a vacuum pump. A good pump is
in the $300 range but you can either get a venturi pump that runs
on compressed air (about $40 from Harbor Freight) or simply use your
recovery pump. It won't create enough vacuum to dry a wet system
but it will get enough air out of a dry system that the system will
You also need a set of service gauges. Lots of mechanics believe
the 134a propaganda and sell their old gauges. I seem 'em all the
time at pawn shops for $10 or less. For under $75 including the
green card, you can be set up to do auto AC work.
For either R12 or R406a, you should get barrier hoses installed if
your system doesn't already have them. If you have barrier hose, it
will say "barrier hose" on the hose. Barrier hose is mandatory for
R406a because the constituent molecules are small enough to go right
through the old stuff. It is HIGHLY recommended for R12. With
barrier hose and an intact compressor, the annual recharge we used
to have to do will be over with. Having barrier hoses and a new
dryer/receiver installed should cost less than $150 if you farm it
out. Taking the hoses off and carrying them to a service shop will
save some money. The old worm-clamp type of hoses are not good
enough to make a completely hermetic system, which is what you're
striving for. Swaged fittings are the only way to go and for that
you have to hire it done by a shop which has the proper swaging
If you have a modern compressor (Sanden, chrysler rotary, etc), then
you're OK. If you have an older compressor (york, long GM, chrysler
V, etc), I recommend upgrading to the modern unit. The shaft seals
really are hermetic, the compressor is more efficient (less power)
and more reliable. A new (not rebuilt) Sanden SD-508 (small),
SD-509 (medium) or SD-510 (large capacity) costs in the range of
$300 retail (much less wholesale if you know someone with a
commercial account). Places like Classic Auto Air sell adapter
plates that let you mount the Sanden on the old compressor
brackets. Since you're having hoses made anyway, fitting hoses to
the new compressor doesn't cost any more.
Once you upgrade your system to barrier hoses and a modern
compressor (stuff you STILL have to do for 134a), you're ready to
load a lifetime charge of R12 or r406a. I do a few things
differently for so-called lifetime charges because I do not ever
want to have to open the system again.
First thing I do is pressurize the system with helium (use the
helium balloon party tanks available widely) to look for leaks. I
put about 100 psi in and leave it overnight. I want to see less
than a 5 pound drop. Helium is the smallest gas atom there is so it
will quickly go through even the tiniest leak. It also diffuses
through even barrier hoses so some pressure drop is OK. If the
system loses less than 5% helium pressure in 24 hours, it will hold
freon forever. Most techs use nitrogen because it is cheap but
nitrogen is diatomic (as is hydrogen, just for those Einsteins who
were going to post to tell me how wrong I am about the smallest
atom), therefore the molecule is large enough not to find small
leaks very well. Evacuate the system before helium charging so that
air and water molecules don't "clog up" small leaks.
Next, I very carefully measure the oil charge after blowing out the
lines with dry nitrogen to remove most of the tramp oil. Enough oil
is vital for compressor life but too much will reduce the cooling
capacity by leaving an excessively thick coating of oil on the
inside of the coils, mainly the evaporator.
Next, I start with a new dryer/receiver. I want as little moisture
as possible in the system. Next, an overnight evacuation. Some
people say this isn't necessary. That was somewhat correct when an
annual charge was the rule. Enough dry refrigerant passed through
the system that minor bits of moisture wasn't an issue. With a
hermetic system, whatever moisture is in the system at charging time
remains. I don't want that. Therefore I do an overnight
evacuation. This gives moisture absorbed in the structure of the
hoses to diffuse out and be removed. I use a lab grade Welch vacuum
pump capable of pumping a 10 micron vacuum. One can get by with
less, trading time for money.
Lastly, I install a vial of fluorescent leak detecting dye. If a
small leak starts, I want to catch it as quickly as possible. As
part of my routine maintenance, I do a quick pass over the engine
compartments of my cars with a black light. I caught a leaky seal
on a new compressor before I either lost the expensive charge of R12
or lost the AC system. Warranty took care of that.
Since with a new dryer, compressor and hoses, the system volume will
likely be different, charging by weight usually doesn't get it just
right. I like to charge by sound, listening to the expansion device
using either a mechanic's stethoscope (2nd best) or an ultrasonic
listener (best). When the liquid line goes solid, one can hear this
by the diminishing of the sound of bubbles. R406a works best with a
little bit of bubbling at the expansion device but charging to just
the threshold of no bubbling will get it close enough.
To give you an example of how this works, I own a 68 Plymouth Fury,
an 82 Caddy for the wife and an 82 motorhome on a chevy chassis.
All have Sanden compressors and barrier hoses. All still have their
initial charges of R12. I converted the Fury 10 years ago, the
Caddy 4 years ago and the motorhome 3 years ago. I made custom
brackets for the Fury because already-made ones were not then
available. I used adapters for the Caddy and motorhome. On the
motorhome, I chose the SD-510 compressor and installed a larger
condenser while I had the system open. Now I get near-freezing air
(~35 - 40 deg) even in 90 deg weather. The compressor consumes no
more power than the old York Vibra-matic compressor it replaced.
The evil incarnate trade group for automotive air conditioning
service, MACS (mobile air conditioning society) has institutionalize
the greed of R134a to the point that most mechanics spout their
propaganda verbatim. Most don't know any better. If you can't do
your own work, you're going to have to search around until you find
a shop not mesmerized by the MACS propaganda.
R134a might be OK for new cars with systems engineered from the
ground up for it - I have no opinion since I'd never buy or work on
a new car - but for older cars, it is death. Done improperly, the
conversion will kill a compressor as fast as if a handful of sand
had been tossed in. Even done properly, the system will under
perform and use more energy.