What is the best source for learning about air conditioning? What are
the best tools to have for charging, evacuation and leak detection?
What O rings and where to get them should be changed? Does the dryer always have to be replaced if the system has been left open? Can a
drier be baked in an oven and then evacuated? How can I get certified to buy R12? Do I need a recovery system to work on the cars?
I have several cars now with broken air conditioning systems and it is going to cost a fortune to get them all running.
Dan the Pod Guy
Been there and done ALL that. I've converted at least 6 cars from R12 to
R134A now, all are still running nice and cold after years of service. I don't
own a shop or anything (I'm actually in the IT business), I just do this myself
along with my brother in our garages. I'm not sure what the best source is to
learn A/C systems. I just learned as I went along. I never really needed leak
detection, I just replaced the drier, all the o-rings, flushed the system,
rebuilt the compressor hoses and changed the compressor shaft seal. If you do it
right the first time, nothing will leak and the system will be good for years to
Even though R12 is a much better A/C gas and cools better (at identical pressures), I would still go to R134A. You don't need any certification, and you can go to Walmart and buy three cans of 134 for $20, good for one car's entire charge. Also, R134A will cool just as well in most situations, but the pressures will be slightly higher. The 928 has a very over designed condenser, so this will not be an issue as it is with many other car makes. Another option is propane/isobutane blend. Many people will tell you that it's explosive and dangerous, but it is widely used in Australia for a few years now and I believe it is now the standard there.
What do you need for A/C service? Wow, where to start, so much to say...
well, you really need the following if you want to do it right:
- Gauges. You need a set of gauges for charging. These go for around $70. There are different adapters for R12/R134A. If you convert to 134, you only need one set.
- All the correct O-rings. You can find from the parts catalog what size they all are and order the correct ones. Some can be found at your local Autozone, others you will need to order from one of the Big 3, or you can go and order a bulk box with most of the ones you need from www.ackits.com or www.acsource.com . If the o-rings have not been changed in more than 5 years or are the old black ones, you need to change them all with green nitrile o-rings (compatible with both R12 and R134A):
- A *real* vacuum pump. Don't cheese out here and get one that connects to an air compressor. You need a true vacuum pump to evacuate an A/C system for at least 45 min - 1 hour. A vacuum pump like this costs $150 -
- If you have the system opened for more than a couple of hours, you need to replace the drier. The dessicant in the drier will absorb moisture from the air and become useless. I wouldn't try to bake the drier to try and revitalize it. A cheap drier for the older 928's costs only ~$30.
- Oil flush. If you're converting to 134, you need to flush the evaporator and condenser with mineral spirits to get rid of old oil. You also need to drain the oil from the compressor. Ester oil should be used for R134A conversions. If you stay with R12, flushing is not required, but I would still drain the compressor and add back fresh mineral oil.
These next steps are more optional, but I would recommend them:
- Replace compressor shaft seal and sealing rings. If you're converting to R134A, or even if the compressor is more than 10 years old, chances are that the shaft seal is about to let go. This requires removing the compressor and disassembling it and purchasing the correct rebuild kit for it. I think '80 - '89 928's have the Nippondenso 6E171 (I know my '86 does). The kit should only cost ~$20. If you are not willing to do this, you should get a rebuilt compressor; those go for ~$200 on eBay.
- An economy crimper. If you're only going to do one car, then you could just go to an A/C shop and have them make a hose for you (or buy them new $$$$). But it sounds like you are doing several cars, in which case it may cost you less to purchase a crimper and make your own hoses and spend less. Old R12 hoses leak more over time and eventually become like sieves, especially the high side from the compressor, and especially with R134A. They now sell a manual crimper that you can turn with a wrench for around $180. I have this one and it works great:
- Bulk A/C hose and A/C fittings. Most 928's have standard (not reduced
size) #12 hose for the low side and #8 hose for the high side on the compressor. The older ones may have standard #8 high and #10 low. Those are the two hoses that usually need to be remade; the other hoses in the system are good for many years. You can get steel or aluminum fittings; the earlier 928's have steel fittings that are heavier but much more sturdy. Here's some hoses:
You will need a shaft seal kit:
And a gasket kit:
Some parts are duplicated in the kit, but it's not like they're expensive.
The 6E171 has 3 large o-rings splitting up the body. I did not replace the one in the middle of the compressor since I didn't feel like splitting it up; I changed only the two on the ends. I also only replaced the head gasket on the shaft seal side that I disturbed (this compressor is a split 180 degree 6 cylinder with a head on each side). Be prepared to scrape the old gasket off the mating surface (usually the old gasket is paper, while the new one is metal).
I can be much more specific if you tell me exactly your plan.
'86 928S 5-spd w/LSD R134A converted too, soon to be test mule for dual parallel flow condensers and Freon cooled intake...
The drier is critical to the operation of the system, and it's not much more
than a can filled with dessicant when you buy it new. After you run the system,
oil migrates into the dessicant bag and it becomes impossible to get all the
moisture out with heat and vacuum. So a new one goes in any time the system has
been opened to atmosphere, since the dessicant will capture moisture from the
air until it's saturated. Moisture in the system will freeze to ice in the
expansion valves, effectively plugging them. Moisture condensed in the bottom of
the evaporator will form a nice acid that will eat through the aluminum there.
Both options are bad. Drier is cheap, compared to those options.
Compressor oil gets poured in before the compressor is installed. Spin the compressor by hand a few times, then drain that out and put new in. Do this a couple times to get any old oil out, then add 6-8 ounces of new oil to the compressor just prior to installation of the hoses and the compressor into the car. Use oil that's compatible with the refrigerant you are using. If this is a conversion, a flush to get the old oil and ash out of the system is recommended before adding the new oil. You are part way there when you clean and flush the condenser out of the car. That may be all the cleaning/flushing you need.
The engine was started. The engine was @ operating temp.
The A/C outlet temperature (@ center bents) was checked. After 10 min. of idling, the temp. of 46°F was observed.
The A/C service ports were dry. The A/C system was evacuated. Total of 787.09 grams of R134 refrigerant was recovered.
The A/C system was vacuum pulled for 30 min. The system was leak tested for 1 hour @ 30 in.Hg vacuum. The system held vacuum for 1 hour and retained 30 in. Hg vacuum.
1030 grams of R134 refrigerant was filled and 280 grams of Polyol synthetic lubricant (ND8 oil equivalent) was added as well.
The A/C system was operated for 10 min. w/ the engine revved @ 2K RPM. The center A/C outlet temp. was @ 41°F. The high side refrigerant pressure was @ ~175 PSI. The temp. and pressure specification is within Porsche specified values.
The vehicle was test driven for 13 miles (in town and on highway). @ the "MAX COLD" setting, the outlet temp. was @ 36°F w/ 75°F ambient temp. The A/C system is operating as designed.