Climate Control

Successful R-134a Conversion

#1
All I can say is that the AC is awesome. Before I reset the antifreeze switch, the ac got down
to 21 degrees F idling in the garage. I set the antifreeze switch to shut down the compressor at
about 42 degrees F, and it ets to that shutdown temperature in about five minutes from starting
the car. I also can't keep the system above the 42 degrees F shutdown temperature. Even with
the front fan on Four (MAX) and the Rear Fan on Three(MAX) with AC on full, the
temperature still falls below 42 degrees F and the antifreeze switch shuts things down (it just
cycles less often - about every four minutes with the fans on full vice every one to two minutes
with the fans on slower speeds). I'm extremely pleased with the results!!!!! Thanks to John De
Pietro for your help.
The best part is that I didn't use any vacuum pump or anything AC equipment (except a 5
dollar charging hose). This great performance is with non condensable gases NOT removed.
All I did was change orings (39.99 from John De Peitro), flush a few lines and the condenser
(flush was 19.99), changed the receiver dryer (some obsurdly low price from David Roberts),
then charge the system with oil and R134a (one can of oil at 4.50 and three cans of R134a at 3.50
a can). Oh, I also had to buy a charging hose and the R134a Adapters that fit on the High and
Low pressure connections (another 8.00 dollars). I didn't evacuate the system, just charged it
up with the system full of air. I then went with my son's Bubble stuff and checked that non of
the systems were leaking. I didn't have a single leak. EASY, EASY, EASY!
I did this not looking for saving a few bucks or save the environment or anything. I just
wanted the system to work. Last summer I had the system fixed seven (yes SEVEN) times.
Even with SEVEN attempts (were talking thousands of dollars), the AC system didn't work.
Winter came, and I just gave up. Since the wonderful EPA said I couldn't work on the system
myself, I had to take it to certified technicians - a total of five different shops (two shops fixed it
twice, or shall I say tried to fix it twice). The result is a total of 28 lbs. plus of R12 released to the
atmosphere by EPA certified technicians (not to mention replacing the receiver/dryer four
times, replacing the high and low pressure lines from the compressor, and more orings and
low/high pressure connections than I can count) . For all you tree huggers, how does you
stupid regulation look now! But, I digress. Because the EPA seems to have a moron clause
preventing anyone with an IQ of over 50 from being certified, I thought I would have better
luck doing it myself. R134a here I come!
So, after filling my system with a less efficient freon and not removing the air in the system, I
got results far better than any of the "professionals". Even just after having the system fixed
from last summer (with R12), the lowest temperature the AC would produce was 58 degrees F.
The longest that temperature lasted from any of the seven repairs was about a week.
Remember, before resetting the anti freeze switch the R134a got down to 21 degrees F (and
probably would of gotten lower, but I shut down the car afraid the high pressures would blow
up the system).
It doesn't make sense how I got such drastically better results with a poorer freon and a
system full of air, but I did.
Another benefit is that after changing orings, components and resetting switches, I learned a
lot about the AC system. Thus, in the future I will have a good idea of where for to look and
how to diagnose any future problems. These really are fabulously engineered (or shall I say
over engineered machines). The AC system is not very high tech (basic refrigeration cycle with
no suprises) and operates using basic thermal expansion and vacuum switches. It's no longer
a mysterious and magical system after working with it.

Todd A. Mauerhan
'87 S4 Guards Red, Cold and Happy

#2
Err, glad the a/c is cold now! But seriously, air or rather the moisture in the air that's in the
system is going to eat it from the inside out beginning with the receiver/dryer and seals. The
water will turn the refrigerant into a corrosive. No kidding. I figure that's how my system got so

contaminated over time (dessicant breakdown) and the resulting mixture ate my rear evap. I
patched it for now, but really needs the same flush you did + evac. then recharge...

#1 replies:
I was worried about this air and moisture being in the system when recharging the system with
R134. I questioned everyone I encountered about this and the consensus was: the air will
reduce the efficiency of the system but a very insignificant amount (this air was referred to as
incompressible gases), and the moisture in the system with R134 isn't near the problem as R12
(the moisture will be a very small amount in the air and will be removed by the receiver/dryer - a
must replace part). The concern about moisture in R134 is not the acid thing but that it if cold
enough and in large amounts will freeze up a line (blocking it) and cause the compressor
overpressurize a portion of the system (I.e. explode, that's why I reset my antifreeze switch to 42
degrees F). Also, as long as the system is opened for only a short amount of time, there
should no problem of moisture contamination. The problem arises when a car's system has a
leak, depressurizes, then warms up and cools down with the starting and stopping of the
engine. This expansion of the air in the lines and subsequent compression draws moisture in,
and it will collect in significant amounts.
I like the idea of having my system evacuated, but I don't have the equipment. I was told
repeatedly that the difference will not be noticeable. Also, to remove the amounts of moisture
present for only opening the system up for a short amount of time would require an evacuation
of the system for about 24 hours (good luck on finding a shop who will maintain a vacuum for
any longer than it takes to see that the vacuum is being maintained). Besides, if I have to let a
"professional" tamper with my system, I'll be back in the same boat as I was with my R12 system
(no one could do it).

#3
It is possible to partially evacuate AC systems without an external pump. I haven't had to work
on my 928 :) - but if the system has fittings for both high and low sides - it goes like this:

Hook up guages (high and low sides), bridge low pressure switch to allow system to run w/out
charge (is there one?), start and run system, crack open high side, low side closed. You should
hear and feel gas exiting red (high) hose. Low side guage should start showing a partial
vacuum! Do this for a while (we're ad libbing now aren't we?) Shut down high side valve. Shut
off vehicle and system. Observe low side guage to see if it holds this 'vacuum'. Charge as
normal.