Roland Kunz

Hello

Porsche used different compressors on the 928.

The early ones contain a viton main shaft seal wich will not survive average R134 PAG oils.

Now on the other side Porsche original PAG is better performing caped oil and not as aggresive as the common used PAG oils.
Now some say that Mineral oil and PAG will not mix and slight leftovers from mineraloil cause trouble so they use POE oils...

Here in germany R12 is absolutly banned since 2000 so you go to refill with R413a or convert to R134. There are no other mixtures allowed in automotive use from the german authorities.

R 413 is also known as Isecon 49.

Some further informations:

<a href="http://www.motorage.com/edindex/0103feat1.htm#top" target="_blank">http://www.motorage.com/edindex/0103feat1.htm#top</a>

<a href="http://www.isceon-refrigerants.com/product/isceon49.htm" target="_blank">http://www.isceon-refrigerants.com/product/isceon49.htm</a>

<a href="http://www.delanet.com/~pparish/retrofit.htm" target="_blank">http://www.delanet.com/~pparish/retrofit.htm</a>

<a href="http://www.epa.gov/ozone/title6/snap/buying.html" target="_blank">http://www.epa.gov/ozone/title6/snap/buying.html</a>
<a href="http://www.epa.gov/ozone/title6/snap/ref.html" target="_blank">http://www.epa.gov/ozone/title6/snap/ref.html</a>
<a href="http://www.epa.gov/ozone/title6/snap/snapdefs.html#unacceptable" target="_blank">http://www.epa.gov/ozone/title6/snap/snapdefs.html#unacceptable</a>

<a href="http://www.aircondition.com" target="_blank">http://www.aircondition.com</a>


Now the reality out there is that you need a good maintained system and a good tech performing the work to maintain good performance.

Doesn´t matter if you go the R134 or the R431 way.
Finally a proffesional is mostly cheaper then blow the compressor. But even then chances for failures are high and thats why Porsche official recomends to renew all parts and swap over to R 134a on all pre 1989 cars.

Grüsse

Snowball the 81 white 928

when you say "early" compressors, i am under the impression that there was one model for the 78 to 79 or 80, then the 6c171 then whatever after that. also, won't quality rebuilds have seals that are compatible with r134a?

Michael Handreck

I've seen claims elsewhere on the Internet that there's supposed to exist a refrigerant called R409A - and it should be compatible with the old R12 (even works with the 'original' mineral oil in an R12 system).
It seems that this (if it is actually true) would be the ideal substitute for R12 as no vacuuming of the system is necessary...

Anyone of the A/C experts heard of this? Comments??

Greg86andahalf

Michael,

You may be confusing vacuuming and flushing. Empty systems always should be vacuumed before refilling, regardless of what type of refrigerant is put in. Flushing is the procedure for attempting to clean out the old oil in preparatin for a conversion.

Greg

Dozman

Porsche, like all other auto manufacturers all recommend to switch over to the new refrigerants, that replace the outdated Refrigerants By 'THE MONTREAL PROTOCAL'. Why, many reasons, Pure profit, to conform to political agrrements, for reasons unbeknown to the average guy.

Take Firestone recall of tires, due to the Explorer. How many people actually know, that The new 'Fords Field' will use the recalled tires as a padding under the turf. Now, one may ask "Who's actually paying for the tire recall?"

Not Firestone, not Fords, But the average Person paying taxes.

John D.

Dozman

Now, since the Montreal Ptortocal came out in early 1993, and started to deal with CFC's. If their findings are correct or not is another story. I can detest now that R12 went thru the roof, as well as many other refrigerants did. The machines that were leaking severly, and vented to the atmosphere, are now tight. What I mean by tight, is that they no longer leak mostly, due to the customer can not afford it. So the machines are repaired. So why make the refrigerants illegal to use. When they could have just made the cost of the refrigerants higher, so businesses keep the machines tight.

The goverment does not make cigarettes illegal, THEY KILL. Everyone knows it. They kill quicker and more than the refrigerants.

So, it comes down to politics and who can make the money. The super rich.

Thats my opinion, and I am always glad to hear yours.

John D.
'85 928 Auto, Black

dr bob

Hi John--

I'm sure that you are correct on the cooling capacity differences between the R-12 and the R-134a. Pretty basic physics, considering the heat of vaporization and the differences in molecular weight. All that said...

The 928 is endowed with a pretty hefty condenser capacity. I suspect that this was a knee-jerk reaction to all the condenser-capacity issues that haunt the 911 cars, but only speculation.

Nobody was more suprised than I when I looked at the performance charts in the 928 FSM that show that the GTS with R-134a actually outperforms the earlier R-12 cars. Look at the evap temps claimed with ~90f ambients, a critical performance range here in the hot climates of Southern California.

So, based on their claim, I decided to reseal my leaky R-12 car, upgrade the hoses, new expansion valves and drier, and use R-134a this time.

The first thing I noticed is that the car is darn cold, based on a very objective digital thermometer in the center vent. It's darn cold because the freeze switch isn't opening at 36f as it's supposed to, so the evap temps are sailing on down low enough to get 21f(!) out of the center vents with 85f ambient at the second fan speed, cruising down the road. Seems that the center vent temp, which is my basis for a performance evaluation, is typically limited on the low end by that switch.

So the decision on R12 or R-134a should not be based on some theoretical system performance limitation with the slightly lighter-weight R-134a refrigerant, because the limitation is not the refrigerant capability, it's the switch setting.


---------------

I do note that John has plenty more experience with AC systems than I do. Most of the work I've done is engineering and controls work related to Rankine energy recovery systems, with 10,000+ horsepower gas expanders used to convert low-temp (~300f) thermal resources into electricity. Like a big air conditioner running backwards. I've only worked on a handful of car systems over thirty-plus years, and only one 928 (mine) so I have to add the "YPMV" to the end.


My subject test mule demo icemaker 928 is a '89 S4 that has fairly low miles on it. The condenser is clean on the outside and the cooling fans function correctly. At some point I'll need to get that freeze switch pulled out and adjusted correctly, so the evaporator doesn't freeze up into a block of ice. Otherwise, it's another summer of frozen fingers on the steering wheel...


YPMV

Jay Wellwood

GAWD....I want your A/C Dr. Bob!

Dozman

DR Bob,

Was wondering a couple things. When you recovered your a/c circuit prior to replacing system components. How much R12 did you recover? How much R134a did you charge into the system?

Ah, reread your post. the new expansion device is definitely a key. I bet with the R12, you could of been able to get down there temp wise.

It's good to hear that I am not the only Sharkster out here with freezzzzzzzing A/C. Its a great thing!

John D.
'85 928Auto, Black <img src="graemlins/jumper.gif" border="0" alt="[jumper]" />

dr bob

John Dozman wrote:

[quote] Was wondering a couple things. When you recovered your a/c circuit prior to replacing system components. How much R12 did you recover? How much R134a did you charge into the system?

Ah, reread your post. the new expansion device is definitely a key. I bet with the R12, you could of been able to get down there temp wise.
<hr></blockquote>

The system was empty due to leakage during longer-term storage. The PO's records indicated dealer service on the AC every six months during the time the car was driven, so I knew that there was some serious leakage to manage. Net: no R-12 was there to recover.

The system was initially undercharged with the R-134a. I don't remember the scale readings exactly, but have that info in notes and on the charge sticker. (I'm not where the car or my records are right now...) I experimented a little with more and less, but ended up light in the end. My big concern was maximizing the condenser efficiency by not flooding it, and therefore keeping the head pressure down at a reasonable level. For those following along at home, the undercharge looks like a light stream of bubbles in the sight glass. But, as John alludes, the only way to make sure you have the correct charge is to do it by weight.

The expansion valves seem to be a key to getting max performance from the 928 system. Owners of cars that have the late style valve can take advantage of the R-134a-capable valve pretty easily. Just buy them. Those with the early style, the one with the threaded nuts holding the hoses and lines into the valve body, may find that their options are a little more limited. Keep in mind that Porsche did not invent any of the air conditioning components in the car, including the expansion valves for sure. So finding an early-style valve with the R-143a curve in it is just a little bit of a challenge, not impossible. DR or Mark Anderson may have them as standard shelf items, I've just never asked.

As far as being able to get the same low temps from R-12, I'm sure it's possible but I never tried. The cost and availability of R-12 at the time was prohibitive and none, respectively.

Of course, since then we've "discovered" that Mexico did not sign the Montreal Protocol document, the one that limits sales of R-12 and the chloro-fluorocarbon refrigerants. In fact, not many countries have signed it. Seems that the list includes countries that manufacture cars sold in the US, but not many more. Anyway, for those willing to smuggle R-12 across the border from Mexico, the cost of R-12 there is only about 50% higher than the cost of R-134a in the US. Cylinders of real DuPont R-12, sold over the counter to anybody with pesos or dollars. I'm not advocating this heinous crime, just letting folks know that it is happening. Of course, I have no need at this point since the car uses R-134a these days anyway.


For Jay who wants my AC, my recommendation is to find a dedicated tech who will work with you to get max performance from your system. Be religious about keeping air out of the system when charging. That means you want to evacuate the system with a good vacuum pump to get as much air and moisture out as possible. Leave the pump on there overnight to boil any last fumes out. Evacuate the charging manifold and the hose to the gas cylinder at the same time. The 928 offers this capability by removing the pressure switch on the drier, and attaching the vacuum pump there while the gas cylinder is attached to the charging manifold.
-----

Folks attending the Devek Gathering in early August may get a clinic on some of this as part of an AC tech session. We did an impromtu session last year that ran well over the allocated time. Marc and Susan do the tech session scheduling, and may decide to allow more time for this stuff. There was certainly plenty of interest. I'll also have the electronic sniffer along for anybody that wants to do a little leak-testing on their car while we are there. I'll be the white-and-pink-haired guy, black S-4 in the SoCal 928 group area. Or, walking around with the camera to grab photos of the fine cars that make it to the event each year.

Snowball the 81 white 928

i used original expansion valve and r134a with no deleterious effect.

dr bob

I don't theink that there's any presumed negative effect with keeping the original expansion valve. The point here is that there are expansion valves that are optimized for R-134a. They give potentially better performance compared to using the R-12-curved valve with R-134a.

The key to best heat transfer is maintaining the mass flow of refrigerant while simultaneously maintaining a very low suction pressure in the evaporator. That's the job of the expansion valve. It's a complex task, and using the right valve might gain you several degrees of evaporator temp reduction.

Compressor capacity and performance also play into this equation, by the way.

Dozman

Actually, I do charge a/c systems differently for different models of cars.

1. Charge system by weight.
2. Charge system by superheat.
3. Charge system by amp draw from the compressor.
4. Charge by weight, then by subcooling, and superheat. Depending on sizes of condensor as compared to system capacity, engineered orfice in place, and efficiency of actual air flow over condensor.
John D.

dr bob

Sperheat, subcooling... kinda hard to predict in a car system. Charge the system based on compressor amps? Still doesn't apply to car systems, unless they have electric-drive compressors. Most 928 systems that I've see have a non-conductive rubber belt drive.

For most cars, and virtually all 928's, charging by weight is th most consistent way to get decent performance, and a repeatable result.


My two sense...

Michael Handreck

As nobody commented on my post on alternative refrigerants, I've looked further into the matter...

It would seem that the conversion from R12 to R134a is not the easiest and best solution, as you need to replace the oil along with all o-rings etc.

Check out this link: <a href="http://www.alltemp.ca/r406a.htm" target="_blank">http://www.alltemp.ca/r406a.htm</a>

Recover the R12, leave the old mineral oil in there, and fill with R406A - done! Maybe this is just hype??

Furthermore, there's yet another alternative: R409A, which is also an R12 replacement and which should also work with the old mineral oil and o-rings etc.

As my car is facing a change from R12 to a 'modern' refrigerant, I would NOT choose the R134a solution and all the problems that comes with it - I would definitely look for a compatible refrigerant...

Try and do a Google search which includes R12 plus either R406A or R409A - at least for a person without intimate knowledge of A/C systems they seem to be just right?

Anyone out there tried anything OTHER than R134a??