Convert AC back to R12?

[McLovin]

This is on an 85 BMW, but would also apply to 80s 911s.

The car was converted fro R12 to 4134 some time in the past.

I took the AC system completely apart, flushed out the evaporator, installed the biggest parallel flow condenser that would fit, high flow Spal fan, new Sanden 508 compressor, new expansion valve, hoses, etc. (In other words, everything is all new except the evaporator, and a couple of short hard lines, which I flushed).

I’ve vacuumed it down and it held at 29.x overnight so I’m ready to charge.

But then I thought this morning, why R134a?

The car was designed for R12, it doesn’t have the biggest system (evaporator, blower fan, air vents etc), and R134a isn’t as efficient.

I’m at a point where I could return and exchange the compressor for an R12 unit and replace one hose, and go to R12 instead of 134. So it’s easily doable, but it’s now or never.

Pros of R12:

(1) All things being equal, it’s going to give me colder air, I *think* that’s a certainty.

Cons:

(1) R12 is more expensive and you can’t just get it at the parts store (counter - I can still get it on eBay and it’s not that expensive any more because there isn’t huge demand any more, most have converted to 134. I don’t love the inconvenience but it’s not something I’d have to buy regularly).

(2) Shops don’t work on it? (I don’t know if that’s true, but I do it myself anyways).

(3) Future buyers might prefer 134? (I’m not worried about future buyers).

Anyone else stuck with R12? Good idea or bad idea?

[Bill5900]

I personally advise staying with R134. It’s readily available. I am more interested in one of the commitments by the US at a recent climate conference to reduce the HFCl by a substantial amount. I can’t remember how much, but enough to drive either new tech or hot beer and sweaty palms

[RNajarian]

I’m sitting on four cans of the stuff from the 1980s and have considered the same thing myself.

[Arne2]

If run at the correct pressures (which are not the same as R12 likes), R134 is MORE efficient, not less. I'm running R134 in the converted factory A/C in my '72 911T, and it works great.

[87maniac]

Have you considered alternative refrigerants?
RedTek, EnviroSafe, etc.

Propane/Butane based, mimics R12 very well.
More efficient that R134.
Much lower pressures than R134 or R12.

You new system with larger condenser, etc would allow
colder temps than R134 without the expense and environmental
concerns of R12.

I've converted several vehicles to EnviroSafe, including
my '87 911 with outstanding results.

[JK McDonald]

Hey McLovin - I've used "Key Board Duster" or "Dust Off" for almost 10 years in the Texas heat with great results. It's formulated to be sprayed into the open air, environmentally friendly, is compatible with all the original R-12 A/C system components and works with mineral oil. The best part is that it's extremely close to being equitable in quantity vs cooling performance with R-12 and cost about $3 for a 10 oz can. The chemical name for R-12 is dichlorodifluoromethane - the active ingredient to look for listed on the can of "Key Board Duster" or "Dust Off" is "difluoroethane". Bring your glasses because of a CIA government conspiracy, the print on the can is very tiny....

Just pick yourself up one of the smaller circular hand held "squeeze to puncture" freon installation tools. The diameter of the "Dust Off" can is slightly smaller than the R-12 can, so may need to add a rubber spacer to the back side of the can. Once you're happy with the evacuation of your A/C system - puncture the can of "Dust Off" at the bottom so you're installing it as a liquid, put in a couple of cans, begin checking your pressures and vent temps.

Works well in Texas - but use your own judgement -
Good Luck - Michael

[fintstone]

Porsche A/C experts could never get my factory system (with R12) to blow any colder than the 50s. It seems not worth the cost/effort to charge a stock system n a 911 unless making mods. My "improved" R134 system ran vent temps in the low 30s. With all the work you have done so far, why would you not run R134 in your BMW (or better yet, replace the hoses with barrier hoses as well)?

[Peter M]

Originally Posted by 87maniac

Have you considered alternative refrigerants?
RedTek, EnviroSafe, etc.

Propane/Butane based, mimics R12 very well.
More efficient that R134.
Much lower pressures than R134 or R12.

You new system with larger condenser, etc would allow
colder temps than R134 without the expense and environmental
concerns of R12.

I've converted several vehicles to EnviroSafe, including
my '87 911 with outstanding results.

I agree, I'm using this for my R12 and R134a systems:
https://hychill.com.au/en/products/minus-30

[tasturbo86]

Consider a new evaporator, or see if you can replace the expansion valve in your old one.
Stick with R134 - works well when properly charged (approx 85% of the factory R12 charge) and it is readily available.
One less thing you will have to explain when you sell the car.
Just my 2 cents

[ganun]

I did exactly what you did, all components except the evap, biggest parallel flow cond , etc. on my car a few yrs ago.
Wife says it's colder than her new Toyota and colder the Audi.
And its on an 89 Peugeot wagon converted to r134.

[GH85Carrera]

If your evaporator is the original one, inspect it closely before you charge it. Get one of the cheap borescopes and run it up under the evaporator from the passenger footwell after you remove the (easy to do) motor resistors. Look for any crud or rust. Mine was full of dirt and just nasty looking.



No doubt it was part of the problem for my pitiful AC before the upgrade.

If you KNOW your evaporator is clean and not looking like mine did, charge it up.

R-12 is a slightly more efficient gas, but it is expensive. Virtually no professional shop will have the equipment to service it. They all threw out the R-12 service equipment long ago. Look on EBAY and you might find the recovery equipment for R-12 so you can service the system in the future and not just dump it in the atmosphere.

You will need to do a full and long flush of the entire system. Cross contamination of the gasses makes for bad results. Most real pros of the era had a separate set of gauges to use with the different gasses to avoid any contamination.

[McLovin]

Wow, that’s one dirty evaporator!
As I stated, I took my entire system out of the car, and apart. Everything.
And all of it is replaced with brand new, including all new barrier hoses, expansion valve, compressor, receiver/dryer, with the exception of the evaporator (which looks like new, still very clean), and a couple feet of hard lines.
The evaporator and hard lines I flushed until they ran clean.
So, it is essentially an all new, fully disassembled and reassembled clean system.
It’s held 29.x pounds of vacuum for days now, so I think here’s no leaks.
I’ve mulled it over and I think I’ll stick with my original plan of R134a, which is what it is set up for.
With the new, modern PF condenser I think (hope!) I should be able to get low 40s vent temps in 90 degree weather.

[McLovin]

Originally Posted by fintstone

Porsche A/C experts could never get my factory system (with R12) to blow any colder than the 50s. It seems not worth the cost/effort to charge a stock system n a 911 unless making mods. My "improved" R134 system ran vent temps in the low 30s. With all the work you have done so far, why would you not run R134 in your BMW (or better yet, replace the hoses with barrier hoses as well)?

Yes, hoses all replaced with brand new barrier hose.

[McLovin]

Originally Posted by tasturbo86

Consider a new evaporator, or see if you can replace the expansion valve in your old one.
Stick with R134 - works well when properly charged (approx 85% of the factory R12 charge) and it is readily available.
One less thing you will have to explain when you sell the car.
Just my 2 cents

Yes, expansion valve replaced with a new one.
I didn’t replace the evaporator. I see no reason for that, it’s just a radiator and mine looks perfect still, zero signs of any leakage, and flows clean, so I can’t see what additional performance a replacement would give me.
And yes, one of the reasons I’ve decided to stick with R134 is it is less to explain later down the road.

[McLovin]

Originally Posted by JK McDonald

Hey McLovin - I've used "Key Board Duster" or "Dust Off" for almost 10 years in the Texas heat with great results.
Works well in Texas - but use your own judgement -
Good Luck - Michael

One thing I’ve seen about that is they add bitterant chemicals to it to prevent people from intentionally inhaling it to get high.
Some express concerns about putting those chemicals in a clean AC system.
Although I’ve also certainly read about a lot of success stories too.
I’m always interested in optimizing performance, but while it does get a bit warm sometimes in my area, it’s no where close to Texas-sized heat.

[GH85Carrera]

Are you adding any condenser area to the system?

Just the two positions only is just not enough. If you want a kick butt AC system, add the two Griffith's condensers in the rear fender. Anything less is going to be marginal at best.

When I first got my car 26 years ago the AC was pitiful at best. The evaporator motor was squealing and squalling like a tom cat fight. I replaced that and the evaporator, and had it in top shape, and it was still just pitiful. I talked to Griffith's and got his entire system. Every item was replaced except the front and rear condensers. I added the two fender condensers, and the hurricane blower and the variable speed fan switches. Now I can be totally cool on the hottest days.

In Savanna, GA in August, My wife asked me to turn the temp UP because she was cold on a lunch time trip.

[McLovin]

Hey GH, I’m a long time 911 guy, I posted here because I know from over the years there’s a ton of AC knowledge here (“Reverse the Flow!!!!” notwithstanding haha).
But this is in an 80s BMW.
That being said, I did upgrade the stock old tech tube condenser to a modern parallel flow, in the largest size I could physically fit in the nose.
I also added the highest capacity Spal fan to replace the very low flow stock fan.
But yes, by going to a bigger, more efficient PF condenser and much higher capacity fan, I think I’ve effectively increased condenser area.

[McLovin]

My car was converted to 134 under prior ownership a long time ago, I’m guessing maybe 10-15 years.
It was what I’d say was a “50 percent” conversion.
They kept the stock compressor, condenser and fan, and I don’t think they took out the evaporator.
Most of the orings were green, but some of the deeper ones, like on the expansion valve and evaporator, were still black.
AND I know the AC hadn’t been touched at all in the last 5 years (no refills, nothing).
AND, when I took out and flushed the evaporator (after removing the xvalve of course) I found it was partially clogged. The flow was poor until the flush fluid and compressed air blew out the clog.
Yet, it somehow actually still cooled somewhat.
I only started to have second thoughts on 134 v R12 because the new Sanden comes factory filled with PÁG oil, and I’m ready to charge it, so I’m sort of at the “point of no return” on 134 v R12.
In doing a ton of reading I’ve found mixed results with R134 conversions, but in the end I think that’s because to do the conversion really correctly, including the hardware choices (upgrading the condenser and fan, etc), the execution in putting it together correctly, and filling it correctly (clean dry system, no leaks, no moisture, no air in the system, correct amount of 134, etc), most DIYers don’t get it 100% right.

[fintstone]

Sounds like you have done everything to ensure a good result with R134. I suspect with a BMW, the surface area is better for you condenser as is the air flow. Also, the hoses are much shorter. I bet it works great.