IcemanG17

Dr Bob
That is quite cold...over a 60 degree differential from ambient...but the broken freeze switch helps too...still very good, especially for R134.
Brian

Ron_H

I agree with Dr. Bob about leaks. Evidently the original German hoses were prone to leaks or it was expected that they would leak. Mine weren't leaking a couple of years ago, but I will change them now anyway in favor of USA made ones. On advice of the AC guys, I changed all O rings last time and they searched for leaks and fixed all they could find. The AC ran flawlessly until I buggered up the compressor.

My latest decision is to buy a Porsche brand "rebuilt" compressor, new hoses, new drier and evacuate the system for a half day. I reasoned that though I could refill my old compressor (spare one) with oil and take a chance on dirt not being in it, if it did have dirt I would lose the expansion valve ($260) and also the compressor anyway ($345 minimum). And no one seems to know where I can find any parts and seals to use if I want to rebuild my own compressor. So out it will come and I will use it as a core to exchange. The AC guys said the Porsche remanufactured compressors all appear to be new, not rebuilt. Yes it will cost more initially and some of my costs to date will be lost, but it will be right and last longer and not leak this way.

So all I need now is money. Does anyone know anybody who would like to buy a red suspension bridge in San Francisco? Slightly used. High maintenance. Cheap. (Hey, don't laugh. I know someone who is sitting in prison for trying to sell that bridge for real.)

WallyP

Hmmm, Ron - I think that you might have slipped a decimal point on the cost of that expansion valve...

Ron_H

That was the price I got from Devek today. Maybe they were off in their quote. That's a somewhat pleasant surprise. I'll call them now and check.
I get their answering machine.

Well, if the valve is only $26, that is the only major thing I am risking by using the compressor that is now on the car. If its not dirty and has enough oil, it should work. And if it doesn't I am only out the valve and the r&r which I would have to do anyway.

I just got Devek and they said the valve was $50.

SharkSkin

BTW, that R&R is a PITA...

dr bob

R&R is a PITA --if-- you fail to loosen the fittings and the hold-down at the fuel cooler. Rigid fuel line connection from the rear of the carat the bottom, hose to the FPR at the rear of the engine. Pull the fuel pump fuse while the engine is running to run the fuel pressure down. Pull the fuel connection off.

If you don't do that, you end up with a pry bar trying to bend the lines enough to get the expansion valve out. If the lines don't pull back into the expansion valve in perfect alignment, ya got yerself a nice place for a leak. Get the cooler loose and everything moves back a lot more easily.

Dave: FYI, on the later cars, the lines into/out of the expansion valve are secured with retainer plates held to the valve body by a couple smaller allen capscrews. MUCH easier disconnect than the early system with the threaded nuts over the tube fittings.

Malibu310

Had mine converted... lost the super cold air.

fst951

Hi Bob.

The problems come down to the fact that the system was not made to run with 134a. We can battle back and forth on this one. Use the factory R12 as it carries the mineral oil better, and out older compressors were made to run on mineral oil and not PAG or ESTER. It is higher viscosity and less corrosive than failed PAG. The other thing is the pressure difference. Take a look at head pressure charts of R12 to R134a and see the potential 80-100 psi high pressure side difference?

That is one thing I don't like at all.

Also R134a has a tendency to leak out faster.

Avoid the blends.

Just my take after a couple of hundred A.C. systems. I don't know everything.....such as adjusting the flapper door, but I sure have learned a lot over the years.

Thanks!

Abby Normal

My R134 conversion in my S3 will blow you out of the car in 100 degree 100% humidity weather. I run the fan on 2 or 3 and it cools great. Other 928 owners that ride in my car always say it's way colder than theirs.... not sure why so many of you say the conversions don't get as cold.

dr bob

I only have experience on one 928 system, my own, so I bow to experience.

The polyolester oil is slightly lower viscosity, but as a synthetic it's less susceptible to localized heating/burning/carbonization. So no ash ever. The POE will coexist with the mineral oil if you don't do a flush. I wouln't put the PAG into any conversion.

As far as the high end of the temp/pressure curve, I'm very aware of the differences. That's why I suggest that only the S4 and later cars are suitable conversion candidates. The big fans make the difference. The later cars ('93+) have a pressuire switch that does dual duty. The diagram for my S4 switch looks like it does the same thing, but I replaced it with the newer one anyway. So if I do have a fan failure that causes high head pressure, the compressor will shut down.

The differences between the factory R-12 cars and the factory R-134a cars are few. There is a slightly different calibration of the expansion valves for the lighter gas. The difference is so slight that the R-134a curves are the only ones you buy today anyway. The condensers were not changed, although they probably should have been. Porsche designed in a whole lot of extra conenser capacity, no doubt a lesson learned from the miserable AC that was supplied in the 911 cars. Otherwise, it's that pressure switch that looks like it changed before the late '93 cars arrived with R-134a anyway. Oh, and the refrigerant oil was changed, barrier hoses were fitted, and different o-ring material to play with the new oil.

Again, the problems that plague most conversions are related to the quality and completeness of the conversion. The same care needs to go into any AC system maintenance or restoration work, no matter which refrigerant you choose to fill the system when you are done. Choice of refrigerant is probably the least worrisome part of the project, all things considered.


With the freeze switch working now, my AC is still cold enough to be uncomfortable unless I put the temp slider up a bit, to between 72 (for me) and 77 (for her). I know several folks who have similar 'problems' with 928 R-134a systems. At least one is a factory R-134a system.


After all that, I can still buy R-134a cylinders locally for a little over $6 a pound, without worrying that it might be recovered or contaminated. I still have a couple cannisters of R-12 that I'm hoarding, and there's enough that I could easily change this car and more than several others to R-12 if I thought it would make a difference. So far there's no reason to my car change back. Maybe in a few years when I'm looking to dispose of 50 pounds of hazardous R-12 waste it will happen. By then my garage will probably be declared a superfund site and the taxpayers will foot the bill anyway.


Stay cool!

SharkSkin

I was aware of the later style expansion valve setup, but thought that started with 87 cars. Another thing I just thought of... Ron has two expansion valves(rear AC) and I'm not intimately familiar with that setup at all. I can't imagine that it's that tough compared to the front expansion valve though... on any year.

dr bob

Changing the rear expansion valve may or may not be important, but it is important that you change the o-rings and the hose sections. So the pass side front seat comes out to get the bulkhead fitting o-rings where the lines pass through the floor, and the o-rings at the solenoid valve there. The lines run under the rear seatand up under the cover for the rear AC unit, so that cover comes out. Secure the rear evaporator on new foam mounts to cure that rattling WYAIT doing the plumbing. New o-rings are needed in the connections just under the passengers footwell/main electric panel, where the rear lines connect to the front section under the car. All together, the rear air section adds a good 2 to 3 hours to the whole reseal project, at least the first time.

WallyP

Expansion Valves:

A/C Expansion Valve 77-86E P/N 928.573.123.02 $28.00

A/C Expansion Valve 86.5-95 P/N 928.573.123.05 $29.45

A/C Expansion Valve - Rear A/C P/N 928.573.123.05 $27.13

All are suitable for either R-134a or R-12.

dr bob

If the late front and the rear have the same part no, why is the price different??...

These are a bargain, by the way, even with the extra $2 for the front. Local places here sell the valves in generic BMW flavor for close to $100.

SharkSkin

I only brought it up because that's another part that would be at risk if contamination(dirt, dust, etc) were to get into the system.