Successful R-134a Conversion
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
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...
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).
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.
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