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Is there an R134a conversion sticker under the hood anywhere?
As @dr bob and @Tom have mentioned, it's a pretty good bet your system has been "converted".
I use quotations because of the sealant putty on your Drier.
What that kind of tells me is that there may be a good chance the o-rings weren't changed out for the proper green ones.
If you unscrew the blue cap, the fitting should look like this.
Screenshot_20260416_154556_Chrome.jpg (275.91 KiB) Viewed 144 times
On the 928S4, the high-side service port is on a bit of tubing just upstream of the receiver/dryer, in front of the condenser on the passenger side. That's the red cap on converted cars. As the OP's pictures show, the low-side service port is on the compressor suction side plumbing from the expansion valve at the evaporator. With everything in place, access is inconvenienced by the upper radiator hose, the air intake hose to the air filter housing at the rear of the engine bay, and a couple cooling system vent hoses that pass to the passenger side fender wall. I used a 90º "conversion" fitting on the low side, and it makes connecting the service hoses a LOT easier.
The little hose manifold plate on the compressor itself has service ports on it, but with the compressor installed there's zero chance of actually using them. Regardless, the Schrader valves in those ports, the o-rings inside the service caps, and the o-rings between the manifold plate and the compressor housing all need to be swapped as part of the conversion. The two between the manifold plate and the compressor escaped replacement (same as: I didn't even know they were there) until the new oil caused them to swell and fail within a day. So dumped the refrigerant charge and some of the oil charge in a matter of seconds. Back to the garage, removed the compressor, new o-rings again including the hoses and the ones that failed, another 24 hours with vacuum on it, then new oil and refrigerant. Fine ever since, about 28 years ago now give or take a couple days.
I have added refrigerant a few times since, last time several few years ago now when I also added a few more ounces of oil to the system. The mechanical shaft seal in the compressor seems to weep refrigerant during hibernation season. Adding a little more oil seems to keep the seal faces wetted longer, reducing the losses noticeably. My initial shake-down drive out of hibernation included a bit of compressor run time, and it's still plenty cold at least on that 65º day.
Thanks again. Not with the car at the moment but will check on Monday. Lots of good info here. I need to check the old records from to PO to see if a conversion was recorded ( I just got this car in November ).
nagykurva wrote: Sat Apr 18, 2026 8:50 am
Thanks again. Not with the car at the moment but will check on Monday. Lots of good info here. I need to check the old records from to PO to see if a conversion was recorded ( I just got this car in November ).
I will get back after doing some digging.
Looks for r134a conversion stickers too. The conversion kits come with them and most people (and virtually all shops) tend to put them on under the hood somewhere...
On the 928S4, the high-side service port is on a bit of tubing just upstream of the receiver/dryer, in front of the condenser on the passenger side. That's the red cap on converted cars.
I knew that.
Not sure why I wrote what I did.
My apologies if I confused anyone.
Absent the details of a conversion effort, there's no telling how it was actually done. The compressor and new drier mentions are consistent with a R-134a conversion perhaps following a problem/incident.
Regardless, it definitely says R-134a was used, and the conversion fittings reinforce that. Since they included a UV dye in a recharge, you can do a bunch of cleaning around your connection under question to remove any traces from your loosening/venting episode, then inspect carefully with a blacklight after it's been sitting for a while. In a dark garage, the dye will show up as a pale yellow/green fog wherever the oil carrier has seeped out. Easiest if you don't drive the car between cleaning and inspecting, as cooling air through the radiator and fans will dissipate the leaking dye. I have a UV "blacklight" LED flashlight (cheap from Amazon) that's quite handy for the inspection duty.
I also have a decent electronic sniffer that detects down to grams-per-year leakage rates. I find it handy to wrap suspect connections with some plastic food wrap with the sniffer probe end inside, and let it gather any leaking gas for easier and faster detection. This is low-pressure side, so no need or desire to have the system running while you look or sniff.
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My car came to me with a pile of dealer service invoices. The pile was a mixed blessing for a car less than 8 years in service; only the dealer had worked on it, but the dealer had worked on it a lot in that time. Most of the services were for testing the AC for leaks, nothing found, evacuate and recharge, return to customer. The seller graciously had the system serviced just before I picked it up, and it was good for about a month before it was again low on refrigerant. The third episode of that drove me to go through the whole system end to end and reseal everything, something the dealer should have done after just a few warranty visits. It was an easy decision to charge it with R-134a after all the flushing, cleaning and resealing effort. I had (and still do have...) a couple cylinders of R12, but it was (and is) a lot more, um, valuable than R-134a as a commodity in the vintage P-car community.
