924Board.org

[emhewitt]

Apparently my A/C isn't working. Hadn't noticed until the last few really hot days. What's involved in getting it serviced? Does that require a Porsche specialist?
Stay cool if you can.
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Michael Hewitt

[924RACR]

One key question: what year car do you have, does it have the factory AC or the aftermarket system fitted to the very early cars?

Really this thread should be probably in the General Discussion; I'll move it over...
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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[924RACR]

More info... on my '82 931, it's got factory AC, very similar but not identical to the early 944 AC system.

As my compressor did seem to still be able to spin - and in fact I'd done a half-fast R134a refit previously, which worked but not well - I decided to do a proper clean and service to get it working well on 134.

The system was already depleted. I installed a new drier.

Having already had 134 in the system previously, it had done its magic on the hoses and caused them to swell, eliminating leaks from the smaller molecule size.

We disconnected all the lines and used some professional grade flushing agent (a good buddy works on house AC systems, same exact principles etc, so he obviously helped me through this) to purge evaporator, condenser, and lines. We did get a surprising amount of junk out of the condenser.

The compressor also got some purging; by applying 12V directly to the clutch, we were able to rotate it manually to make sure we got any remaining junk (old oil etc) out of it.

After all this flushing, we reconnected all the original components (plus the new drier), with all new green (viton?) AC o-rings and some blue thread sealant designed just for refrigerant circuits on all the fittings and o-rings.

Pulled a vacuum and let it sit for an hour, as per the book... then filled with oil and 134 to the same amount specced for the 944, figuring it would be about correct for this system being close enough in size to work.

It did, and works quite well even though the whole system is designed/sized for R12...
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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[Beartooth]

I'm actually working on the AC on my 560SEC, bringing it back to life after a hiatus, and I'm sticking with R12. Fortunately, it had a little pressure in it, and I think that’s a determining factor when deciding whether it’s time to replace a bunch of stuff or if a less intensive job is worth the risk. I'm almost done with it. I started by flushing most of the system. Acetone is great for the evaporator and condenser if you can pull them, but I think it’s a risk on any soft parts. And your flush gun may not like it and decide to blow it past the seals... AC flush products are the safer choice here. I replaced all o-rings and seals (including in the compressor), replaced the expansion valve, and finished with a new receiver/drier. I found a little corrosion, but the compressor turned freely and was clean inside, so I’m not too worried about it.

I stuck with R12 because the system works poorly as-is with R134. It's mostly the condenser - a tube-and-fin unit. They usually don’t work well with R134, but they do flush out easily, unlike the newer ones. The other Mercedes (the SEL) I upgraded to a newer condenser, and it works ok with R134 now, but that was a chore. I haven't laid eyes on a 924 condenser, but it may have enough head room to handle R134; an upgrade would probably help, regardless. I was able to get a case of R12 at $25 per can recently, and I think people overstate the expense and difficulty of finding that. It’s worth a look and a probably a fairly minimal expense as long as the system is tight.

Partly because I just like doing it myself, I've got a gauge set, vacuum pump, and a few other tools (even a leak sniffer, just because I got a good deal on it) so I can do a whole job myself. It's not too hard to figure out, for anyone interested. On the other hand, if you find a good shop willing to work with you, most of the labor can be handled yourself with common tools, then you’d have to take it back to be checked over and charged.

I have to throw in something on oils since this is something that confused me a lot back when. Double end-capped PAG is probably the best choice and will work with either refrigerant. People get confused and think it won't work with R12, but that's because it reacts poorly with mineral oil, not R12. If the compressor is replaced and comes with PAG, I’d flush the rest of the system and stick with that regardless of the refrigerant. The go-to for retrofits is POE, but POE has a big drawback and does nothing particularly well. It’s highly hygroscopic, and if you’re having a shop finish the job, let them handle adding the oil rather than adding it yourself and leaving time for it to absorb moisture. Mineral oil is probably what you'd choose if you stick with R12, but I’m not sure about the quality of the stuff you can still buy. Because of that, I decided on the SEC to give PAO a try. It's fully synthetic, compatible with R12 and R134, and non-hygroscopic; it could be the ideal choice if PAG isn’t an option (which it probably isn’t if the compressor is original; there’s an ounce or two of oil you’ll never get out of it). That said, I’ll have to run it successfully for a while before I’ll recommend it.

Anyway, the irony is that, for as much as I love a good AC system, I’ve got no plans to put one on my 931 – I just want to keep that light and I’ll drive another car (the SEC, soon) when it gets too hot. But if I lived in blazing heat like some of you, that would probably mean not driving it all summer long, so I get it.
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1980 931 diamond in the rough

[924RACR]

Good point on oils; I'm trying (and failing) to remember for certain what we used with our 134 conversion, but PAG sounds right to me.

My 931 is a street/highway cruiser, going for luxury, speed, and looks, so weight is very much not a priority... and yet until I get some tint on her, the AC is merely struggling to fight away the worst of the heat, so it's still not great in the real worst of the summer (temps above 85F),

So it's definitely a fair argument of if it's worth bothering on these cars...
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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[Glemon]

I went through this with my 924S, I don't know if it is the same as an early 924 or 931 or not. I tried charging it first with R12 and it worked for about a week. So I decided the system worked but something leaked. So I leak tested it, repaired a switch that was leaking, out in all new seals...There is a long story here, including me screwing up and not realizing I had the temp control on fully warm I stead of fully cold when first testing it, but...

Anyway I ended up with Red-Tek R12a (they call it that, don't know if it is the official name). It is basically propane mixed with some other gases, it acts a lot like R12. Yes it is flammable, so is the gas your car runs on. Anyway I was have trouble pulling a vacuum (related to my tools available, not the system) and discovered the R12a didn't need it, so I tried it. The cars has been running cool for almost two years now, anyway, the stuff I used seems a little more friendly for DIY on old cars so thought I would mention it.
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88 924S
68 TR250
02 IS300

[Beartooth]

Good point about window tinting. I need to refurbish my back frame/glass (it's delaminating and the seals are half-gone; I just live with it since it's a fair-weather car), and I definitely plan to tint that. I did that on my SEC with Huper Optik ceramic tint (50%, I think). I've been happy with it so far, and it does help with the heat. Something like that on a 924's back glass would make a big difference. You'd want to avoid the cheap cosmetic tint that doesn't actually block much heat; the good ones reflect half or more of the heat without even getting that dark. Anyway, just that back hatch allows a lot of heat in. Didn't the 928 actually have an optional secondary evaporator to help with that?

The use of propane (or blends with propane) as a refrigerant is something that has tended to be a hot topic on other forums I'm on. I've never done it, but I don't see a problem with it as long as one can be certain the evaporator and anything else inside the car isn't leaking. Exterior leaks should be less of a problem. I have heard you can use any old propane, although the Coleman or other cheap stuff might not be that clean. I'd consider it, although the fire risk is something to keep in mind. I don't think it's a drastic risk; the trouble is, unlike fuel lines, you're talking about something not designed to be protected in an accident. I will say it's likely to perform better and less likely to end in a blown compressor than a R134 retrofit done poorly. I'd still evacuate the system (you can borrow/rent a vacuum pump from Autozone and the like), although you could probably get away with just charging if the system still has some refrigerant in it.
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1980 931 diamond in the rough