I did my A/C conversion to R134a last August. All of the old R-12 had already leaked out.  I removed the compressor and drained out the oil and replaced it with Castrol A/C conversion oil from the kit mentioned below, removed the condensor and cleaned it out completely using paint thinner and compressed air, removed and cleaned the expansion valve, and then reassembled everything with new O rings. I used the Castrol 134a conversion kit [$35 at Pep Boys] that is designed for the German cars, including the shark. After pouring in the oil [before reinstalling the compressor] and converting the valves, I vacuumed it down for several hours to dry the system.

I purchased a meter and hoses specific for 134a from Pep Boys, and using them I charged the system with no more than 80% of the amount specified for R-12. I actually did it to a specified pressure that I found on an A/C list or maybe it was on this list.  Unfortunately I don't remember what the final pressure was. Anybody know what it is supposed to be? Final cost was less than $100.

Here's the update: It still blows nice and cold even with the hot Southern California summer desert heat [and yes, I was in Phoenix awhile ago, and it worked there, too, where it is really hot.]
Dan Shapiro

Just completed R134a conversion on the 86.5 shark.

I decided to replace the old system and convert to R134a because the old system was the original equipment, had required several service visits, and the compressor was leaking badly ... plus my local Porsche shop (Bob Dumont in Oklahoma City) couldn't locate a rebuilt Nippon compressor.
Also, I'm signed up for the 928OC convention in Wichia and it tends to get hot there in July.  It's not cool to sweat on leather!

After speaking with Charlie at Griffiths Tech, Inc. and discussing my various options, I ordered a kit for about $650, and had it drop shipped to Dumont's.  The new kit (which can also work w/ R12) includes a more efficient Seltec compressor w/clutch, new bracket and fittings, double wall hoses, O-rings and dryer.  Estimated installation time is four to five

Charlie was very helpful and knowledgeable at the time of purchase, but was even more helpful after my mechanic had installed everything and couldn't get the output below 60 degrees.  (Mine was the first R134a conversion my mechanic had done on a 928.)  Charlie took the time to talk directly with my mechanic to resolve the problem, which was due primarily to an overcharging. The recommended R134a charge is about 80% of the R12 charge by weight.

See you in Wichita,
Mark May

I went though the same thing and ended up with about 60% of the R-12 amount being optimal. I think most don't realize that you don't need as much 134A as R-12 OEM specs.


No "Conversion Kit" from Autozone is going to do you much good I'm afraid.
The parts you'll find there that will help are the charge hoses, gauge manifold, polyolester refrigerant oil (in the plastic bottles, not the stuff mixed with R-134a in the metal pressure cans), and the charge port adapters for the new gas.  From DR or Mark Anderson,  get the o-rings, the drier, and expansion valve (2 if you have rear air).  You'll need access to a good vacuum pump to suck the air and moisture out when you are done. You'll also want to get some R-134a, a little over a kilo according to the factory conversion instruction. That can come from Autozone I guess.
Jury is hung on whether the hoses need to be replaced with barrier type for use with the R-134a.  I decided to bite the bullet and get the hoses rebuilt with the new stuff.  Another option is to get the hoses new from Charlie Griffiths at www.griffiths.com, or from one of the Big Three parts vendors.  I think Charlie has a whole conversion package less gas-- worth a look and a call.

If you are experienced with auto AC,  nothing in the car will surprise you except the number of o-ring connections, especially if you have rear air. If you are not experienced,  you may want to refer the work to somebody who is.  Mistakes are quite punishing financially.
My 928 134a conversion is awesome cold, one of the best conversion results I've seen.  Done with care,  it's a great investment.

dr bob

At 09:26 PM 4/2/01, Roth, Richard wrote:
>My mechanic buddy says that nothing special is needed for a R12 to R134 conversion; just flush the old oil and load in the R134. ALl this 'nonsense' about parts compressors etc is just BS
>Somebody give me some ammo to tell him where he is wrong.

First, a general statement: A system that is converted from R-12 to R-134a will lose some cooling capacity.

In general, he has a good point. In the case of the 928 in specific, he is wrong. The 928 A/C system has a LOT of O-rings. Every joint in every line, every connection - all have O-rings. These black rubber O-rings are ten to twenty years old for most of us. They are hard, brittle, and already leak with R-12. If you put R-134a in there, with its smaller molecules, leaks
are assured.

The receiver/dryer will contain enough old oil to cause a problem, and if the system will be open for a couple of hours to change the O-rings, a new receiver/dryer is mandatory.

In my opinion, a minimal change from R-12 to R-134a includes:
Leak test the system while it has R-12 in it - repair all leaks.
Change all (or almost all) O-rings. (This will help with the leaks above.)
Empty the oil from the compressor, flush it if possible. Put fresh oil in.
PAG (polyalkylene glycol) is better oil, but isn't compatible with the mineral oil that is in the R-12 system. POE (polyol ester) oil is compatible both with the mineral oil/R-12, and the R-134a, so it is normally the best choice for a change-over. Install the same amount as what was drained out.
Blow the oil out of the condenser, flush it if possible, checking for free flow. Add 2 ounces of new oil.
Install a new receiver/dryer.
Install the new charging fittings for the R-134a.
Evacuate the system to a hard vacuum, using a good vacuum pump. Leave pumped down at least two hours.
Charge the system with R-134a, using approximately 80% of the amount of R-12 specified.

In my opinion, R-12 is better, but more expensive. No matter which of these two refrigerants you use, the condition of the system is the main thing that determines how cool you are.

Wally Plumley
928 Specialists



I'm hoping someone on this list knows how to add this to the 928 OC tips page under the air conditioning section as it may be helpful to someone in the future.  I just replaced my A/C O-rings this past weekend (OK, I still have a couple more on order) in the process of converting to R134a and will be having the system leak tested and filled next week.

Here's a list of part numbers, sizes, and numbers of O-rings I found in my car (88 S4 with rear A/C):


part number size(mm)  front rear
999 707 284 40 6.6 x 1.5   2
999 707 247 40 7.5 x 2 4 3
999 707 261 40 9.0 x 1.8 2  
999 707 250 40 10.6 x 2 3 1
999 707 251 40 14.0 x 2 3 4
999 707 252 40 17.0 x 2 2  

And here's where they're all located:

Front A/C:

1. expansion valve (under plastic tray next to intensive washer    reservoir): 2 x #251, 1 x #250, 1 x #247.

2. return line from expansion valve, middle of firewall: 1 x #252.

3. compressor fittings: 1 x #251, 1 x #250.

4. other side of return line to compressor at low side fill valve:    1 x #252.

5. heading into condenser: 1 x #250.

6. bottom of condenser heading up to receiver/drier: 1 x #247.

7. pressure and temperature switches just before receiver/drier:    2 x #261.

8. at receiver/drier: 2 x #247.

Rear A/C:

1. expansion valve: 2 x #251, 1 x #250, 1 x #247.

2. solenoid valve under passenger seat: 2 x #284.

3. 2 pipes under car from solenoid valve to front connections:    2 x #251. 2 x #247.

The kits I got from 928 Specialists were a bit different, but I've updated them with this information so they should have it right now.
Thanks to Wally, Jeannie, and Dave for all their help!

Greg Klanderman


I just converted from R12 to R134a last week - I replaced all my o-rings, (except the two at the firewall) and the receiver dryer. I did not replace the expansion valve, although it would be easy to do so.

The Porsche tech bulletin for retrofitting (number 9501) specifies the following parts for 1987-1989:

Receiver Dryer 944.573.943.00
o-ring 7.5x2mm 928.707.247.40 (I actually replaced about 12 of them, don't remember the exact count. Remember to coat with fresh oil before installing)
High Pressure Valve 928.573.965.03
Low Pressure Valve 928.573.965.00 (I actually used adapters instead of changing the valves - $12 @ Autozone) 300ml +/- 20ml of Esther oil
2 Labels 964.701.141.02 860g R134a (1030g w/rear air)

The entire procedure took me about 8 hours total, but I took everything off the passenger's side of the engine (compressor, smog pump, brackets ..etc.) and cleaned everything while I was in there.. Otherwise you could probably do the entire thing in about 2-3 hours.

I had my mechanic evacuate the system (before) and then re-fill it when I was done.

So far the A/C works very well and doesn't appear to be leaking anywhere.
It held vacuum for 15 minutes before being filled. (After being drawn down for an hour)



There are NO good reasons to convert a 928 to r134a. Converting to r134a is NOT an upgrade.
Some one liners to support my reasons follow. There are more technical reasons than I am willing to list here for not converting. Usually it boils down to two reasons that you want to convert.

1. Cost. That is not a valid reason anymore for 928 owners. The cost of
R12 is falling as people stop using it. It is not as cheap as r134 but well worth the difference due to reliability, performance and longevity of the system. Last summer I paid $15 a pound. It is probably cheaper now. If you have someone install R12 for you, it may be cheaper, since he can put in the recommended amount and be done. With r134, you have to play with the charge to make it cool the best. That takes time, and time is money. With R12, you can leak up to 6 oz before performance is affected. With r134, 1 oz will affect performance. All older HVAC systems leak a little, yes, even after you replace all the o rings and hoses and compressor seal. (I can't beleive that the hose between the receiver drier and expansion valve gets replaced. It looks like you would have to pull the engine to replace it, especially if you have rear air). If you have rear air, don't forget all the hoses back there.

2. Can't DIY. Wrong. Many sites on line will issue a license for mvac AC for ~$15-$25.
You don't have to know anything about MVAC to get a license. It is all about handling R12.

Note that I am talking about 928s. If you have an old beater (not 928) that you will trade or junk in the next few months, and you don't care if you are the worst PO ever, then you can put any of that Freeze12 or
R134 trash in to make it cold for a few months as it destroys the compressor.

Actually, the 928s with the 6 cylinder Nippondenso (MY '80 to '90) will run more than a few months on that crap because it has one of the best systems ever made. But it will fail, since only R12 will transport oil properly through the system.

I have not converted any 928s for the above reasons. I did install one Griffiths replacement compressor with r134. That Denso was destroyed by running it with low charge.

If you notice a reduction in performance, check the sight glass. If you see bubbles, turn it off until you recharge. The R12 transports the oil and when you run with low charge, you starve the compressor of oil and cooling. The pressure switches do not provide adequate protection.

I am now starting to convert 928s back to R12 after the owners get fed up with r134. I guess that should be called an upgrade.

If you are a tree hugger, note that it is still controversial and r134 will be banned soon.

Earl Gillstrom '91 GT


Earl is 100% right about avoiding as much as possible an R-134a retrofit.

Unfortunately, the average home mechanic does not possess the required skills to properly service and diagnose vehicular a/c systems. Most car mechanics that I've met have no idea as to what they're doing when it comes to auto a/c systems and rely heavily on their Snap-On gizmo to guide them. Keeping this in mind, R-134a utilizes Polyolester compressor oil which does bad things:

  1. Absorbs humidity, which is the number one enemy in a refrigeration/air conditioning sealed system
  2. Does not work well with older rubber hoses and O-Rings. Handling this oil requires much care.

A simple vaccum of a sealed system which contains polyolester oil may not be adequate in entirely removing humidity.

Another important fact to note is that R-134a is less-efficient than R-12.
What does this mean? In refrigeration, everything is based on pressure-temperature. Pound for pound, R-134a's efficiency in transferring heat is far less than that of R-12. The newer cars that use R-134a possess larger condensers and evaporators to make up for this reduced capacity.
Early R-134a vehicles had many problems in maintaining temperatures as manufacturers were still using the R-12 components; upgraded only so that they would be compatible with the polyolester oil but still undersized in capacity.

There are many that have performed such conversions but have maintained their stock rubber hoses. Unless they are of the newer neoprene based rubbers, these hoses may eventually leak or burst but not before contaminating the entire system with residue.

In my opinion, as a refrigeration contractor and, whatever it's worth to all, I would try to maintain the R-12 systems. If R-12 is no longer available, there are replacement gases specifically designed for vehicular a/c systems which are not harmful to the ozone layer and are basically drop-in refrigerants. Beware as some of these drop-in refrigerants contain propane or butane and are not approved for automobiles but are designed for the commercial refrigeration market. Since many of the drop-ins are blends of various combined gases and not necessarily azeotropes, a leak which may develop on the high side of the system may in fact imbalance the chemical properties of this gas blend and thus may require complete recycling/disposing followed by a fresh new charge of gas. A small price to pay as compared to converting to R-134a.

Early sharks lacked sufficient cooling. Later sharks '89+ possessed a more refined a/c system but unfortunately never quite performed perfectly due primarily to the fact that the solar heat gain on our "aquariums" was simply too much for the a/c system to handle.

Using a good leak-finder or dye will also aid in minimizing leaks. My suggestion is to find an experienced auto A/C shop that can guide you in the right direction. If he's good and you're happy, stick with him. Price should not always be considered as the decisive factor in choosing a reputable firm.

Andy Evangelidis
'91 928S4 horizon blue/cobalt
PCA-Rennsport Region Canada


On 2/28/2012 9:20 AM, Brian Scudder wrote:
I just had my compressor and 2 hoses rebuilt on my '87 928S4. I'm staying with R12 (I have several cans). I plan on replacing all the orings with the official Porsche
orings from the dealer.

Is R12 oil still available? Is the "R134/R12 compatible" oil really compatible? Or will I need to do a system flush and replace all the oil?

When assembling the connections should I lube the orings with the oil?

The orings for the low pressure switch, 900.174.011.40, is NLA, and the temperature switch, 999.707.261.40, is over $12(!) Anybody have a source for these? Or, I'll just leave them alone...

Brian - trying to stay cool this winter in TX
'87 928S4
'83 928S track car - for sale
'86 928S project car

Nothing special about "Porsche" O-rings. Just get the correct size in green or blue O-rings from your local parts store. The reason for using green or blue is that they are good for R-12 or R-134a, so if you or the next owner ever change over to R-134a you won't need to change them. Change every O-ring that you can get to.

Always oil the O-rings with the oil used in the system.

Yes, mineral oil is still available. There are three refrigeration oils for automotive usage - mineral (R-12 only); POE (good with R-134a, OK for R-12); and PAG (good with R-134a, not usable with R-12, installed in most new R-134a systems). I would suggest that if you are staying with R-12, stay with the mineral oil.

Wally Plumley
928 Specialists