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.
Thanks
Dan the Pod Guy
Portia's Parts
==========
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
come.
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):
http://www.ackits.com/merchant2/merchant.mvc?Screen=PROD&Store_Code=AMA&Product_Code=21-24708
- 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 -
$300:
http://www.ackits.com/merchant2/merchant.mvc?Screen=PROD&Store_Code=AMA&Product_Code=90059
- 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:
http://www.ackits.com/merchant2/merchant.mvc?Screen=PROD&Store_Code=AMA&Product_Code=71550
- 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:
http://www.ackits.com/index.cfm?fuseaction=bulkhose
And fittings:
http://www.acsource.com/index.asp?PageAction=VIEWCATS&Category=209
You will need a shaft seal kit:
http://www.acsource.com/index.asp?PageAction=VIEWPROD&ProdID=104
And a gasket kit:
http://www.acsource.com/index.asp?PageAction=VIEWPROD&ProdID=107
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.
Dan
'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.
__________________
Bob Fuelleman
______
charging report:
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.
Mike