1976 911 AC Freon question

[Borg76]

I have a 1976 911 that I inherited from my parents. They purchased it new and it has remained unaltered. It's a real beauty, garaged in the winter and has less than 37k original miles. It's super fun to drive but my wife would like some AC versus the windows. It has the original AC but of course it's blowing warm air. Can I still get a freon that will work versus retrofitting something more modern. I'd like to keep it original as much as possible. I'm not the mechanic that my dad was but am very capable. Any hints would be most appreciated.

[colingreene]

First thing to do is either buy AC gauges and see what is in it or take it to some one.
Its strongly likely that even if it has any freon in it that you will have problems as soon as it runs.
The seals seem to dry out when they sit.

As an alternitive you could look into the AC solutions kit that is for the 3.2 and see if it could be adapted to your car if it has the front and rear condensor, replace the ancient compressor and drier and have a 134 system.

Not knowning where you are R12 could be hard to come by for the older style system.

What kind of budget did you have in mind for getting this stuff working?

[Duc Hunter]

In many cases it's near impossible (and expensive) to get R12. Ask around, maybe you can. Also by now the hoses may be dry rotted and leak. Shops in Europe fill systems with Nitrogen to look for leaks. Great idea, and every time I mention it here in the states they look at me like I have 3 eyes. Using vacuum wont catch everything as vacuum pulls holes closed, pressure opens them. Anyway, a pressure test would tell you how leaky things are. I suppose you could use air to pressure test.

My guess is you would need new hoses and a new compressor. The refrigerant has oil in it that, with regular use, keeps the hoses and compressor in good condition. Getting new hoses and a compressor rated for more modern refrigerants (R134 etc) is probably easier than R12. I would think someone like Griffiths would make hoses or a hose kit for your car.

[GH85Carrera]

With 50 year old rubber hoses, you will really want to replace them.

Contact Griffith’s Porsche and let Charlie make his suggestions. The stock AC is pitiful nut better than nothing unless it is really hot. Stock ac is fine for night time.

R-12 is going to be hard to source, but it is out there.

It is all easy DYI, except for the charging. That takes some gauges

[EC900]

Congratulations on the acquisition. Post a photo, love to see original examples.

There should be a sticker somewhere on the rear lid that will determine the Freon refrigerant spec or if there was any conversion probably in last 30 yrs since R12 was outlawed, or some literature in the owner’s manual was the original system had. Comparing to a modern car, the R12 ports are smaller than R134a.
I had a new 91 Honda w/R12 that had to be converted in 1996 (large evap leak) because of the industry transition to R134a was in affect and R12 was getting scarce even back then.

I too agree with colingreene, take it to an AC shop and at very least first get it pressurized. Good chance there’s a leak, dry rot seals and the aluminum fittings have a tendency to corrode over years….decades.
Dealer installed or factory?
There’s a bit of difference between the two. Dealer installs were rough installs, chopped a hole in the passenger side foot well.
These AC units were never a superior system whether factory or dealer installed VPC units, going through the expense of any diagnostics and repairs, satisfactory results are going to be iffy especially on the sunniest of hot summer days.

Another thing to consider is the engine and exhaust - whether or not you have a 5 blade fan and thermal reactors which create more engine heat (for emissions burn off) then adding the ac compressor to that load… in a traffic jam or city stop n’ go, might be a long term detriment.

You going to be better off budgeting for a modern system.

[1989Carrera]

I guess I'll be the lone dissenter. I would have the system evaluated by someone that's been in business long enough that they are proficient with R12. I think it would be to your advantage if you find an independent Porsche shop that specializes in air-cooled 911s. Your '76 should have the non-factory Behr under dash system. My '77 had that system. I live in Houston where a typical summer day is 100+ degrees F and 100% humidity. Even in these conditions I got 34 degrees F out of the vents when driving and 38-40 degrees F when stuck idling. R12 is not rare and is not difficult to source. I don't know where you live, but if you live in the US you can buy R12 all day long on Craigslist and Facebook Marketplace. Today the price per 12 ounce can ranged from $20-$70. My Behr non-factory installed system required 28 ounces of R12 so I only had to buy (3) 12 ounce cans.

When I purchased my '88 I couldn't believe how bad the AC was. Especially since a month prior to my purchase the owner spent $5K replacing the barrier hoses with Griffiths' barrier hose set, compressor, evaporator, expansion valve and drier. What I didn't realize was at that same time the system was converted to R134a. On a summer day at 100+ degrees F and 100% humidity I got 54 degrees F out of the vents when driving and 65-68 degrees F when stuck idling. All I did was sweat. It made it so I had to pick and choose when to drive it based on the weather. After putting up with it for a while I made the decision to revert the system back to R12. After flushing the system more times than it probably needed, I installed a new drier, removed the R134a adapters from the compressor manifolds and added the correct amount of Ester oil to the compressor. After that I purged the system with nitrogen and then pulled a vacuum overnight. The next morning I purged the system with nitrogen again and pulled another vacuum overnight. After filling the system with R12 I was able to achieve even better vent temperatures than I did on my '77. On a summer day at 100+ degrees F and 100% humidity I get 32-33 degrees F out of the vents when driving and 37-38 degrees F when stuck idling. I attribute the better results to the '88 having a front condenser and condenser fan that the '77 did not have.

That's just my 2 cents. I see no reason to do the required modifications and spend the amount of money it takes to make an inferior R134a system put out "acceptable" vent temperatures.

I have no desire to be scolded or debated about how bad R12 is for the atmosphere. At least I capture the R12 using a refrigerant recovery machine at a small independent shop near my home. It's been 6 years since I reverted back to R12. I've had zero issues and have not had to add any additional R12.

[Duc Hunter]

Originally Posted by 1989Carrera

I guess I'll be the lone dissenter. I would have the system evaluated by someone that's been in business long enough that they are proficient with R12. I think it would be to your advantage if you find an independent Porsche shop that specializes in air-cooled 911s. Your '76 should have the non-factory Behr under dash system. My '77 had that system. I live in Houston where a typical summer day is 100+ degrees F and 100% humidity. Even in these conditions I got 34 degrees F out of the vents when driving and 38-40 degrees F when stuck idling. R12 is not rare and is not difficult to source. I don't know where you live, but if you live in the US you can buy R12 all day long on Craigslist and Facebook Marketplace. Today the price per 12 ounce can ranged from $20-$70. My Behr non-factory installed system required 28 ounces of R12 so I only had to buy (3) 12 ounce cans.

When I purchased my '88 I couldn't believe how bad the AC was. Especially since a month prior to my purchase the owner spent $5K replacing the barrier hoses with Griffiths' barrier hose set, compressor, evaporator, expansion valve and drier. What I didn't realize was at that same time the system was converted to R134a. On a summer day at 100+ degrees F and 100% humidity I got 54 degrees F out of the vents when driving and 65-68 degrees F when stuck idling. All I did was sweat. It made it so I had to pick and choose when to drive it based on the weather. After putting up with it for a while I made the decision to revert the system back to R12. After flushing the system more times than it probably needed, I installed a new drier, removed the R134a adapters from the compressor manifolds and added the correct amount of Ester oil to the compressor. After that I purged the system with nitrogen and then pulled a vacuum overnight. The next morning I purged the system with nitrogen again and pulled another vacuum overnight. After filling the system with R12 I was able to achieve even better vent temperatures than I did on my '77. On a summer day at 100+ degrees F and 100% humidity I get 32-33 degrees F out of the vents when driving and 37-38 degrees F when stuck idling. I attribute the better results to the '88 having a front condenser and condenser fan that the '77 did not have.

That's just my 2 cents. I see no reason to do the required modifications and spend the amount of money it takes to make an inferior R134a system put out "acceptable" vent temperatures.

I have no desire to be scolded or debated about how bad R12 is for the atmosphere. At least I capture the R12 using a refrigerant recovery machine at a small independent shop near my home. It's been 6 years since I reverted back to R12. I've had zero issues and have not had to add any additional R12.

Now that is very interesting. No scolding here. I seem to remember that R134 was not as thermally reactive, or what ever the proper term is, as R12....meaning is cannot absorb as much heat. I agree in some states like Tx and Fl R12 can be easier to find. In states like California or NY though....very expensive and tough at times.

Your experience has me wondering if I should try to run R12 in my Classic RetroFit A/C as a test....or many my Renoir (like a Griffiths) system, and see if it improves things. Would be an interesting test for sure. I am sure teh R134 hoses would work with R12, and have no clue what else I could need to change. Hmm..

[kuehl]

This could be a fun thread for sure.
Where is Willy when we need him most?

[kuehl]

Capability to absorb heat:
Latent heat of R134a = 68.2 btu nominal.
Latent heat of R12 = 89.3 but nominal.
This in simple terms means R134a pound for pound can absorb more heat.
Hence, larger evaporator, and more condenser capacities.

Excessive non-condensable gases (aka "air") in a system
with either R12 or R134a reduces their performance.
Hence, large systems (stock 911 or improved 911 with more condenser and
evaporator capacities) requires purging of the system with either refrigerant gas
that is recovered, or with nitrogen before pulling the final vacuum helps to
reduce non-condensable gases.
Ideally a micron gauge should be used to determine the vacuum depth level.

[rwel]

Borg, some books and forum threads emphasize that ac systems are (necessarily) sealed systems. Which is to say, the refrigerant doesn't get "used up"...it leaks out. Yours did. So solving for the leak(s) which exist in your car will be fundamental to resurrecting your ac. 50-year-old hoses are certainly a prime suspect, but hardly the only suspect. Griffith's hose kits, and his other components, certainly get solid reviews on these forums. My '81 SC's ac cools moderately for about two weeks before the R-134 leaks out. Putting in more is clearly pointless until I fix the leaks.

I completely resurrected the ac system on my '88 BMW M6. No complete kits existed, so I made my own hoses, among many other changes- fans, condenser, etc. It was time consuming, but not terribly difficult. I also leaned heavily on Rob Siegel's excellent book Just Needs a Recharge, which covers your questions and much, much more. Like the pros and cons around choice of R-134 versus R-12 and the appropriate oil PAG (R-134 only) or Ester (OK for either, thus allowing you to go back to R-12 if 134 doesn't cut it). R-12 is attainable, but you have to be sure of its purity, as some that is sold on Craigslist, FB, etc. is probably recycled and very possibly contaminated. Pure, brand new R-134 is available everywhere.

Lots of choices and considerations. As others have advised, gain as much knowledge as you can, either through finding a shop that can handle your project, or educating yourself and DIY'ing it. Griffith's is widely praised for being helpful, and producing quality stuff. I haven't been a customer yet, but may in the future. I knew zilch about automotive ac, but I learned, then successfully rebuilt and improved my M6 system. It was a very rewarding project, and I will probably go after my SC's system next.

Good luck.

[Duc Hunter]

Originally Posted by kuehl

Capability to absorb heat:
Latent heat of R134a = 68.2 btu nominal.
Latent heat of R12 = 89.3 but nominal.
This in simple terms means R134a pound for pound can absorb more heat.
Hence, larger evaporator, and more condenser capacities.

And there goes my idea out the window. To my low IQ brain this means R134 can take more heat out of the car more quickly, and there for cool more quickly. I guess will stick with R134 and save myself a lot of time. I love this board!

[Koizumi]

I won’t mention Enviro-Safe. Oops! I did! Boy has my car been chilly for more than a decade! More than R12. Especially with the Industrial version.

Paired with Griffith’s evap fan, it’s a literal walk-in freezer for me.

Ok back to the regularly scheduled program

[kuehl]

Safe? lol

https://www.epa.gov/snap/envirosafe-finding-violation

[Racerbvd]

[Koizumi]

That was 2013. Filing issues are always issues. That’s why it is legal to apply to r-134 systems and not r12 systems. Either way I’ll let this go as it’s certainly controversial. I didn’t mean to stir the pot.