FredR

Is there an adjustment factor for fill quantity of refrigerant when changing from R12 to R134 by any chance? Never thought to ask this question but it may be relevant if the two gases have different characteristics.

Anyone any idea how much a system fill should take with the rear a/c option for R134. I seem to remember stock is 1.2 kg.

Regards

Fred

joejoe

I believe you use 80% of r-12 charge.

dprantl

Porsche specifies how much R134a refrigerant should be put into a 928 system in TSB 89501. It is 1030g for an S4+ with rear A/C.

Dan
'91 928GT S/C 475hp/460lb.ft

FredR

Dan,

Thanks- just dawned on me when I saw yournote that it is probably specced for the later GTS's for which there is an amendment in the manual -durrgh!

Having an early GTS originally equipped with R12 I forgot about the later ones which physically are more or less the same with a different drier bottle arrangement I seem to remember.

This begs another question-though- as my system has a slight leak- takes about 4 months to need a top up- does anyone have any idea how much I might be able to safely overfill by to help delay the need for a refill?

Fred

Ducman82

i just had mine done. took 1.7 pounds of r134. works great

dprantl

The TSB is actually for retrofitting Porsches with R134a that used to contain R12. However, I do believe the '93-'95 GTS R134a quantity is the same 1030g with rear A/C.

I would not overfill the system at all, especially not in the climate you're in. Also, don't refill it too many times or you may find eventually your compressor will not run so well and it will blow your climate control relay and/or melt the A/C clutch. This happens because you slowly lose A/C oil along with the refrigerant leak. You will then need a new compressor.

Dan
'91 928GT S/C 475hp/460lb.ft

dprantl

I am assuming you don't have rear A/C. It would work even better if you put in another 0.2 pounds, which would be 860g as specified by Porsche.

Dan
'91 928GT S/C 475hp/460lb.ft

Ducman82

At least I think it was that......... I'll have to check with the shop again.. Lol.

GregBBRD

'94/'95 GTS with rear A/C take 37 ounces, of R134a.

FredR

Give or take a few grams that is 1050 gms. The only reason I a interested in a small amount of overfill is to compensate for leakage and make the charge last a bit longer but I have no idea how much over charge the system can tolerate before it is deleterious.

We have done a couple of oil dye/UV tests and cannot detect anything so I rather fear it is slowly leaking from the evaporator.

Regards/thanks

Fred

FredR

Thanks for the concern- I've been playing around with the 928 a/c system for nearly 15 years- I usually allow about 2 or 3 top ups and then start again from scratch- blow it out, vac it, fill with oil and gas type of thing.

I think German car a/c systems have improved somewhat. My Cayenne a/c system works fine [touch wood]. The Japanese cars I have had last ages without need for gas and our Kia Sorento does OK as well.

It would be interesting to know if anyone has owned a 928 without a/c gas loss problems!

Regards

Fred

dr bob

Fred--

Find an electronic sniffer and search again.

I tried the UV Dye method and it's hit-or-miss depending on location and leak size. It also depends on oil leaking with the gas as the dye comes out. You get to search for the mini oil slick that glows in the dark. A good electronic sniffer will detect leaks at the grams-per-year rate. Make a gag for joint testing with a plastic bag wrapped around the joint, sensing tip inside with the joint to improve sensitivity. Compressor seal leaks are more common than evaporator failures, and virtually impossible to fid with the UV method unless the leak is massive.

FWIW, avoid the electronic sniffers that "auto-zero" or recalibrate themselves on the fly. They tend to zero-out a tiny leak in a minute or two, treating it as background.

dr bob

On the gas loss problem, I have mine tight enough to go years without attention, so long as I drive the car and use the AC regularly. If I pull off for a project someplace for a month or more, the charge depletes slowly. Shaft seal is the offender in my case, and a new seal didn't do anything to improve the situation unfortunately.

FredR

Dr B,

Thanks for the thoughts. I fully agree about use being important. I religously use mine at weekends in part for that very reason but what the tolerance threshold for seal leaks is I really do not know other than it is a problem. Similarly I have no clue whether the amount of use factors in. I have always assumed that brief useage does the trick and that just a few minutes of use keeps the seal face wetted but maybe that is not the full story. I always tell my friends in Europe to use the a/c during the winter months for a minute or so during use.

I had the compressor rebuilt with new body seals and new dynamic seal and that has most definitely helped. To be fair, I do not know what seals were used - OEM or after market. If they went cheap then maybe that is starting to leak a bit.

My Subaru Legacy had a Nippon Denso compressor in it - it was a relatively noisy thing made worse by the fact that on a flat 4 motor the a/c compressor sat high up front so the nose bounced off the hood. Used and abused that car for 10 years as my daily driver and apart from a small electrical problem that thing never missed a beat in 100k km. Thus I have assumed that it is not the compressor that is the problem but maybe that is just not the case although why I have no clue.

An interesting thought on the UV detection and sniffer systems- have used both. I find the UV method seems to work well on static seals perhaps less so on dynamic seals. The local a/cshops tend to work on the basis that if they cannot find a static leak it must be the main compressor seal but of course they cannot see the evaporator.

It is all a real PITA! a/c is not a nice to have over here- mine stopped working just before I got stuck in a traffic snarl up!

Regards

Fred

Schocki

Both my GTS and my 944 S2 have two R12 systems converted to R134a. Both conversions where done by myself and I used 80% of the refrigerant capacity stated in the manuals for R12.
I drove the converted 944 and GTS in Texas and never had a problem.

The most important part during a compressor rebuilt are the o-rings that sit on top of the compressor. They hold the adapter for the hose connections. The o-rings on the high pressure side get thin over the years and refrigerant will start to leak eventually.

I would consider my AC in the GTS to be leak free. It needs service every 3-4 years by filling in exactly one can of refrigerant, that´s it. I recently fixed my comb flap and footwell vacuum actuator leaks. The GTS produces a center vent temperture of about 36º F now at an outside temperature of 85º F. I think that is pretty good.

My only cars that never needed any refill in the AC system were our family cars (always HONDA). Our recent model is a HONDA FR-V (not sold in the US). 2006 model and I own it since 2007, ice cold AC with no need to be serviced soon...

I recommend to my fellow Porsche 928 owners in German to not turn the AC off at all. The more you use it, the less trouble you will have (my experience). You can always counter heat