streetsnake

So the a/c shop didn’t want to tackle the ‘79 retrofit/update. Looks like I’m going to have to try to do it myself. Not excited. Any advice would be appreciated. Mainly worried about replacing the dryer without breaking anything and getting the line run that connects behind the computer. Speaking of that line, I purchased 2 new lines from griffiths, both linked below. I guess, I’m missing one line. I believe it is the one circled in the PET below, but I couldn’t find a part number. Can anyone help me with that or tracking one down?
https://griffiths.com/product/928573...-barrier-hose/
https://griffiths.com/product/928573...-barrier-hose/

Rob Edwards

Your circled hose is the rubber section of the whole high-pressure line, it's # 35 on that diagram, 928 573 093 03. Will not be available new from Porsche, your best bet is to remove the hardline from the car and have a local hydraulic shop replace that section.

GregBBRD

We also make a hose that can be substituted, instead of removing that line from the car.
You will need to silver solder on a fitting to the brass line.
We do this with a MAP gas torch, in the car.
Requires a bit of care to not burn anything nearby.

streetsnake

Does it have to be replaced. The a/c guy was telling me that all the rubber lines need replacing when converting over to r134 because of molecule size, however, I’ve never read others doing this. @GregBBRD hose sounds great but I don’t have the know-how or tools to do that. I’d end up ruining something for sure.

Rob Edwards

My vote is to keep the system as R12, which is still widely available at roughly $30-40 per lb. You need 1050 grams, less than $100 worth.

FredR

The original hose is not suitable for R134 that needs a barrier hose to prevent fugitive emissions. The normal operating pressure in that hose is somewhere around 230 psig depending on ambient conditions so osmething t be taken seriously. The existing hose however is saturated with mineral oil and that acts like a barrier. No self respecting ac engineer will endorse reusing that hose in R134 service however i have done this on two 928's and it seems to work fine but I would not even attempt this on new R12 type hose even if it was available free of charge. The trouble is Porsche did not fit a union in that line [they could easily have done so] and it looks to be nigh on impossible to do anything with the engine in situ albeit some have.

Another approach is to simply cut the line and use a proprietary compression fitting to fit the revamped section back in. Some folks do not like these things- I reckon they would work OK. The alternative is brazing a new fitting and good for those that know what they are doing but I would not trust myself with a MAPP torch in such a location.

copperstew

In Rob Sielgel's book "Just Needs A Recharge" he says that the leaking molecules theory is overblown: "The concern that the original R12 hoses would leak E134a like spaghetti strainers appeared to be somewhat overblown." (p.27)

He goes on to say that if the system was operating correctly before switching, you probably don't need to replace the hoses. He says to replace all the o-rings, the receiver-dryer, and then the oils and R134a refrigerant.

He also notes R12 cools better than R134a so if you can find cans of R12 (new-old-stock) then that could be an option.

A shorter summary of Ch. 2 can be found here: "Air-conditioning dos and don’ts" (Hagerty 2018)

mj1pate

I can’t speak to the non-barrier issues of the flex portion of the long pressure/suction lines, but plan on taking your time with this.
Replace all the orings, drier and the expansion valves. That’s a job in itself.
The pair of short pressure/suction lines that connect to the compressor should be barrier. Griffiths can sell OEM equivalents. You can save a hundred on this pair by having Cauliflower or similar hydraulics shop make these barrier hoses.
Pressure test the system. Listen for leaks at each junction with a mechanics stethoscope and then do soap bubble tests at each.
If the above tests pass, you may have enough confidence to go forward with R12. BUT unless you swap out the old compressor, you may be leaking R12 into the atmosphere.

Petza914

Look on Craigslist for a canister of r12 and stick with that. It's a more efficient refrigerant.

gazfish

Would the shop not even pull a vacuum to see if your system is ok currently?

streetsnake

No, but I might be able to reach back out. He did jump the compressor to see if the clutch engaged, which it did. He looked things over with me and explained how he would do it. He’s an older guy that’s been doing this for 30-40 years and I believe he may be a 1 man show. He can pic and choose what he wants to do.

Eplebnista

Read this: Uncle Otto's guide to 928 AC

Scott Peterson

You can get a vacuum pump for 100 bucks from harbor freight and gauges for 50 on amazon. Replace all the O rings and then use this Envirosafe stuff: Enviro-Safe Industrial R134a Replacement 8 oz cans & cases | Enviro-Safe Refrigerants, Inc. (es-refrigerants.com)
And if you read the anything on the EPA, almost all of the "R12" they find coming into the US is a hydrocarbon anyway. You might as well buy the Envirosafe stuff for 12 bucks and use that. It runs at a lower pressure than R12 and WAY lower than R134, so your compressor will live a long time. It is more thermally efficient than R12, so it blows colder, and has bigger molecules than R12.
Or you can use "Freeze 12" Refrigerant Freeze 12 – Frosty Freeze A/C Products Company (frosty-freezeacproducts.com)

Eplebnista

Enviro-Safe is flammable. Old 14 and 16 ounce cans or R12 can be found on Craigslist, Ebay, Facebook marketplace etc. I had a stash of those until I bought 15 lbs. of R12 from someone I trusted.

My Harbor Freight vacuum pump still works fine after pumping down 6 or 7 systems. If it were me, I would flush the system, replace the o rings, hoses and receiver-dryer. Pull the rubber boot off the underhood duct and check to see if your evaporator is blocked with crud. You can get hoses rebuilt at a hydraulic hose shop or DIY using fittings described in the document linked above. Use Ester oil when refilling as it is compatible with either 134 or R-12.

monkez

Lot's of great recommendations . Unfortunately, I had to do a full blown conversion. This just means that if a noob accountant nerd like me can pull it off, you can too.

The only thing i will add is
1) buy a $20 UV LED black light and go looking for leaks. Also, when you put in new refrigerant, try to use one with a UV additive so you can find leaks if they occur and
2) Research your oils, especially if you upgrade to 134a! A previous owner of my car didn't and it looked like some bozo just put r134a without any kind of work or prep. As a result, everything was a big gooey, congealed mess that had to be completely flushed and the compressor rebuilt.

Good luck!