re: R134a conversion

[Yojedi]

The subject of R12 and R134a for our aging AC system has been much talked about here. I searched the forum and have found lots of useful information to finally schooled myself to the point of being "comfortable" about undertaking AC related project. Now comes the fun part ... I am going to convert the system to R134a!

My car is an '87 535is. AC is running but not cold. Compressor and clutch appear to be in good working condition and hoses look in decent condition. I inspected refrigerant level through the dryer sight glass and observed streaks of fluid which tells me refrigerant is very low. Based on these findings my preliminary plan of actions is as follows;

1. Remove and replace dryer (R12/R134a compatible)
2. AC system flush (before reinstalling new dryer)
3. Pull vacuum of the system to discharge old refrigerant and any fluid. Also test for leak.
4. Recharge system with R134a

So far so good? Actually I do need your input on some minor details;
1. Are there any o-ring seals that should be upgraded to R134a compatible? If so, where are they in the system and where do I buy these R134a compatible O-rings?
2. Lubricant oil ... spec calls for 170 cc ... is this in addition to what's already in the compressor? What oil should I use for R134a system?

Am I missing anything else? Hopefully I can get these last of details resolved so I can proceed with conversion with confidence. Thanks guys!

[elwessoE28]

Personally if the system appears to be working (clutch engages, seems to build pressure, no leaks), I'd try Freeze12. I used that stuff on my E28 a long time ago, and for the effort/cost, it worked really well. AC would only be "cool" sitting at idle, but once you were moving it worked great. Probably $30-$40 kit from online will get you back to having cold air instead of messing around with all that shenanigans. I think there's other R12 "replacements" out there that drop in and are good, probably equivalent to Freeze 12.

I designed refrigeration systems and dealt with this stuff far more than I care to admit... All refrigeration systems are designed for the refrigerant and oil to mix, this is what lubricates the compressor, so oil + refrigerant is constantly traveling thru the system. When engineers design refrigeration systems, making sure you have good oil return no matter the operating condition is critical to longevity.

The real headache here R12 system use mineral oil. R12 and mineral oil are miscible, but R134a and mineral oil are not miscible, so if you replace just the refrigerant and not the oil what will happen is oil will accumulate usually in the condenser and eventually run your compressor dry (also mineral oil and PAG oil, which is what R134a systems use, cannot mix). The trick is to get all of the old oil out of the compressor, condenser, and evaporator. The seals/etc compatibility is based on the oil, not the refrigerant (R134a is no more "harsh" than R12 or other refrigerants). Normally in retrofits you use ester oil, since that's miscible with R134a, R12, and mineral oil.

[Yojedi]

Personally if the system appears to be working (clutch engages, seems to build pressure, no leaks), I'd try Freeze12. I used that stuff on my E28 a long time ago, and for the effort/cost, it worked really well. AC would only be "cool" sitting at idle, but once you were moving it worked great. Probably $30-$40 kit from online will get you back to having cold air instead of messing around with all that shenanigans. I think there's other R12 "replacements" out there that drop in and are good, probably equivalent to Freeze 12. .

Isn't Freeze 12 flammable?

[Mike W.]

From what you said, I'd look on Craiglist for some R12, it pops up every so often. Charge it with a can or two of it and you should have decent performance. If you go the R134a route you really need to upgrade the condenser to a parallel flow to get good cooling. A few have said it's ok, but most people are not at all satisfied without a condenser upgrade. Even an overpriced can or two is cheaper and much easier.

[elwessoE28]

No it is not...

http://www.mye28.com/viewtopic.php?t=92465

It's actually mostly R134a, with some R142b to help with the miscibility. Probably best to get as much of the R12 out, put it under a real good vacuum, and then recharge with Freeze12. On my E28, I topped it off and drove it like that for at least a year and it was fine.

Even if it was flammable, I wouldn't be very concerned about it. Propane (R-290) is used in some commercial applications, and is considered a "green" refrigerant since it's not considered ozone depleting. They put a limit of about 3lb max charge in any given circuit. Propane has a pretty narrow range of A/F ratios in which it will burn and also requires much higher temperatures than other hydrocarbons. Take into consideration that the engine bay is pretty well ventilated, it would be pretty unlikely that you'd ever have an issue.

[jhh925]

Normally in retrofits you use ester oil, since that's miscible with R134a, R12, and mineral oil.

If the remanufactured compressor you bought comes with that glow-green oil, is that ester oil? Just curious.

[buzby]

I personally would stay with R12 as Mike suggested. Especially as you have an original "non messed with" system. I refilled my M5 with R12 and mineral oil and performance is great! Used existing Bosch Behr with new seals, clutch bearing, etc. New filter drier.
Only issues I have is the AC blower seized up from lack of use.....
Stay away from equivalents.

Dave

[Yojedi]

I personally would stay with R12 as Mike suggested. Especially as you have an original "non messed with" system. I refilled my M5 with R12 and mineral oil and performance is great! Used existing Bosch Behr with new seals, clutch bearing, etc. New filter drier.
Only issues I have is the AC blower seized up from lack of use.....
Stay away from equivalents.

Dave

R12 definitely is a more straight forward route. Just hope getting R12 can be as straightforward Anyhow what kind of mineral oil do you guys use and how much to use? Bentley manual says 170cc but did not clarify whether that included amount needed for compressor.

[dcains]

R12 is easy, although not all that inexpensive, to buy on eBay, despite the warnings in the listings about needing a license. But why bother? R152a is your new friend, it's icy-cold, and it's cheap.

[demetk]

But why bother? R152a is your new friend, it's icy-cold, and it's cheap.

Why bother? You can't teach an old dog new tricks.

[boomslack]

But why bother? R152a is your new friend, it's icy-cold, and it's cheap.

Why bother? You can't teach an old dog new tricks.

For both of y'all, can you use r152a in an r12 system? My AC got luke-warm a couple months ago (right before cold-season so I wasn't too concerned ... I switch it on every now and then to let the compressor run). Is there an advantage to switching, aside from the obvious? My system is, to my untrained eye, pretty much entirely unmolested ...

[dcains]

Much lighter load on the compressor with R152a - I can barely hear mine.

[demetk]

I have the same experience as dcains and am very satisfied with it's R12 like performance.



Unfortunately if you're not a DIYer, I doubt if any a/c shop will want to touch this stuff.