85 BMW - Convert BACK to R12??
 

My 85 BMW was converted to R134a, like most cars from the 80s.

I took the 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.

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?

Well only point of converting back if the 134 wasn't cooling as R12 was. R134 is not as efficient and runs higher / high pressures

Check this but I think the two require different oil in the system, will need to change that.

The compressors come with oil in them.
The system hasn’t been run yet, so if I swap out the new R134 compressor for a new R12 compressor, the oil is automatically correct.

There is a formulation used in Canada - I THINK it is 90% propane 10% Isobutane. Direct replacement for R12.

Forgot the brand name.

Obviously flammable.

Cheap.

If you want to pick my brain PM me.

The replacements are RedTek and EnviroSafe
(propane and butane mixture)

Conventional R134 and R12 are Very flammable.
And produce Phosphene gas when burned.
NASTY STUFF!

That is correct. Plus I believe the o-rings will need changing. I had a 1985 635csi and the A/C was broken when I got it (compressor had seized). IIRC there wasn't much option then but to convert to 134 which required changing oil and o-rings.

https://www.duracool.com/Duracool/refrigerants.html
Been running this my 944 for years.

Here is what I’ve done with every single old car that I’ve worked on in the last 10-15 years, since my easy source of R12 dried up. I bring it to my friend’s shop, who has an A/C machine, we replace components as necessary, (or not if not), and he vacuums it for 10 minutes and then fills it with R-134. I think that he adds some oil but not sure.

It works EVERY SINGLE TIME, and I have cold A/C for as long as I own the car. I’ve never had an issue related to the R-134. No changed parts, no changed hoses or O-rings, nothing. YMMV but that is actual experience and lots of it.

Interesting! According to everything you read, that has little chance of success.
Yet, there you go.
My job, where every little detail was sweated over, and everything replaced with new, should be spitting ice cubes when I’m done!

I have had similar experiences to Speeder . Just send it ! No hoses, no o rings. Check , and repair system for leaks, or locked compressors, etc, evacuate, change over fittings , vacuum down for 30 minutes or so, and fill to 90% or less capacity with 134. I will usually quit filling when it gets cold, and the gauges are right where I like to see them . I think less is better here .
Unless the system has small leaks, it almost always works . With the exception of old 911's

Since you went parallel stick with R134.

rjp

Actual experience = 100% success rate. My buddy has probably done hundreds of cars at this point. Exactly as Fred describes.

I am pretty sure you need to add oil to your new condenser and to your evaporator, at least I did when adding new parts. Need to find out what oil is supplied with the compressor PAG ( polyalklene glycol) or POE (polyester oil), POE is compatible with 134A and R12, PAG is only recommended for R134A.

Is your new expansion valve designed for 134A or R12?

My experience as well. Except with 911s. Apparently due to so much hose, so many connections, and such poorly placed condensers.

Expansion valve is for use with 134a.
Per Sanden, no additional oil needed.

http://forums.pelicanparts.com/uploa...1632850376.jpg

The systems people do with 911s are crazy.
It’s like a rolling condenser showroom display! :D

So looks like your compressor is shipped with PAG oil, I do not think it is compatible with R12, with the proper expansion valve the 134A should be pretty cold. Being an old BMW I would worry more about the engine overheating, LOL.