Should I convert my A/C back to R12?

[Sam Thompson]

So, last year I converted my 1986 BMW 325es to r134a. I replaced all the seals, some lines, replaced the condenser with a parallel flow unit, rebuilt the compressor, replaced the expansion valve, and the receiver drier- basically all new; however, I haven’t been too impressed with the performance. It has never really blown cool. So this year, I bought a new expansion valve to re-replace the one currently in the car. But then, my neighbor gave me 2-ish cans of r12. I have heard the e30 A/C systems work much better with r12, than with r134a. My question is if I should go back to r12 provided I find another can, or should I keep trying to get the r134a to work? One thing I noticed was that the system held a charge over the winter (Yes!), and It doesn’t seem to want to take more of a charge. When I measured the pressures last year, the low pressures were too low, and the high were too high, which made me think expansion valve, but it could be something else.
Thanks!

Topic

[Andrew Phillips]

I would leave the system as R134a. Why? Because if you have any AC trouble in the future you may not be able to get any more R12 and then you’d have to convert it again. The performance of an R12-to-R134a converted system will never operate as effectively as it did on R12 because of the differences in the properties of the refrigerants. R134a requires more gas volume than R12 did, converted systems do not have the capacity to allow enough gas volume for it to work the way it did on R12.

[Daniel]

+1

R12 is banned in most states now. So, yeah, You won’t be able to get it any more. Just bring those cans of R12 to a local shop so they can dispose of them in a responsible manner.

[Gary]

R12(Freon) is a superior refrigerant that provides longer and much better cooling than R134-A, however, it has been banned for manufacture since 1996 and supplies are getting scarce. You must also have a 609 certification to buy any of the remaining R12 supply.

[Bluesnut]

I’ve done a number of 134 conversions and have had very few problems with getting them to cool properly.
What were the approximate low and high side pressures on the car both at idle and at raised RPMs?
What is the static pressure? (Meaning engine and A/C off with both low and high sides stabilized?
Did you pull a vacuum on the system before recharging?

One of the cars that I did putz around with was one of mine. It cooled well but my opinion was that it could be better so I made my own orifice tube (’87 Ford) and it was unbelievably cold after that.
On a 100 degree day it would put out 25 degree air and after 20-30 minutes I’d find myself turning the fan speed down to keep from freezing. I was actually stunned to see a 70-75 degree drop from the ambient. Definitely not the norm but nice. 🙂

[Sam Thompson]

I can’t remember the pressures exactly, but I seem to recall that the high side was something like 290-300, and the low side was something like 150-180 at idle. Resting was something like 90 psi. I put in approximately the amount of refrigerant per a BMW r12 to r134a service builtin. I evacuated the system before charging it. Now that I think about it, the receiver drier may have been open to outside air for a short time (day-two days), but I evacuated it for quite awhile. What could be the symptoms of an over-charged system?

[Sam Thompson]

I don’t have direct access to a set of manifold gauges, so right now I’ll just have to tell you a few of my observations. First, the system produces a temperature difference in the lines. The one going from the compressor to the condenser becomes incredibly hot, and the line from the evaporator to the compressor is cool, but not cold. Secondly, I notice little vent temperature change when I turn the system on, or leave it off. Thirdly, last year, it seemed to cool by about 15-20 Fahrenheit, but after my (stupid) attempt to boost the amount of refrigerant in the system, as I thought it lost some, it doesn’t do that much. How best can I remove refrigerant from the system, as it is illegal to let it go into the air. I though about taking it to a shop, but one place told me it would be $125 to take out the refrigerant. I thought that was crazy.

[Bluesnut]

Pressures will vary a bit based on ambient temperature, humidity, airflow, how many bugs are in the condenser,,,,,,,, 🙂

Based on a lot of past experience, the static pressures on a properly charged system usually run about 120 or so PSI. That means with the engine and A/C off and after sitting for while to allow pressures to stablize.

High side should be roughly in the 240 or so range and low side around 35-40 PSI. The high side may be higher in some place like Arizona in the summertime.

Offhand, it sounds like an overcharge, some moisture still in the system, or possibly some air entered during the charging process after the vacuum pump was disconnected.
The line from the evaporator to the compressor should be pretty cold and if it’s humid at all where you live it should be sweating also.
Is the condenser reasonably free of bugs and not too many mangled fins? Are the cooling fans operating as they should be?

As to legalities I understand your point. Removing refrigerant is pricy and part of that is due to government regulations which require shops to spend a ton of money on a refrigerant recovery machine, getting people certified, and so on.
As to bleeding some refrigerant off (and I’m not condoning it…) I will say that it happens all the time and a system with a leak is essentially doing the same thing.

‘-

[Mike]

A couple things.

First, I love that you have a E30. I have one that I daily drove for 5 years, but has rusted out pretty good and corrosion took out my fuse/relay box and I need a vehicle wiring harness for it. It’s expensive and difficult to find one that’s uncut. I can’t let it go, it’s been sitting in my yard for almost a year. So sad, but I can at least watch videos I took of driving it to reminisce. It’s the best car I ever had. I wish I had got one back when I got into cars instead of my Jetta. If I had built and taken care of a E30 like I did my Mk2, I would have one hell of a car in my garage (the Jetta is a hell of a car, but there’s just no holding candle to a E30).

Second, getting on topic, keep in mind that automotive AC refrigerants have changed roughly every 20-29 years. That just happens to be the length of time that patents can be made to last. Draw your own conclusions on that one. The point being that performance or toxicity are not the primary reasons for change.

Third, The professional A/C service sounds expensive but it’s not. See, the system is designed to be run with a precise amount of refrigerant in it. Professional service is the only reasonable way to do it correctly. It’s one of the few instances in car repair where is not cheaper to buy the tools to do a job then pay a shop to do it. It can be done properly 2 ways. First method uses manifold gauges, a bulk R-314a tank, refrigerant scale, vacuum pump, oil separator, and a oil/dye injection tool, ($1000+ roughly) and the guy doing it needs a thorough understanding of AC system operation (be worth paying well). The other way is to use a fully automatic machine that incorporates all those tools into one automated unit that is very expensive ($3000-$6000) but able to be operated by someone with limited knowledge/skill. There’s no cheap way to do it or have it done right.

If you’ve spent the time/money to do all that work, it’s absurd that you don’t want to have it professionally serviced. I would, however that you do your own research on the ideal refrigerant and oil capacities (because you’ve done custom work and the guy doing it would have to guess how to deal with it) and specify to the shop what the system capacity is. Also keep in mind at least half, but not all of the oil is removed during professional recovery, and one should not inject the full system oil capacity when doing a normal service.

I got my E30 without a complete AC system so I don’t know anything about your situation from personal experience.

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