Resurrecting vintage A/C can be cool, if you know what you’re doing

Despite winter’s consistent attempts to reach out from its icy grave, it is (technically) spring. Driving season is almost upon us. Many of us rush to complete winter projects so we can get our baby out on that long ribbon of endless asphalt.

As some of you know, I have a particular predilection for automotive air conditioning work. Some folks find that odd, as a) I live in Boston, which, temperature-wise, ain’t exactly Death Valley, and b) I live and breathe vintage BMWs, which don’t have a reputation for having cold A/C. In fact, in these and other vintage cars, where the A/C didn’t really work all that well even when it was new, there’s a kind of chest-beating that many owners exhibit. Rather than fix the A/C and replace the original R12 refrigerant with R134a, some folks say, “I ripped the A/C out to save weight. Now, for refrigerant, I use R75/2—75 mph, two windows down.”

Now, if that’s what you want to do, that’s fine. But I’ve never been an adherent to that philosophy. I am so not an R75/2 person. I’ve gone hard the other way. Even though Boston doesn’t have unending months of flesh-searing temperatures, it does get hot here in the summer, and when you combine that with the snow-and-salt roads of winter, the driving season gets pretty short if you don’t want to use your vintage ride in uncomfortably hot temperatures. Even if you don’t mind the heat, your spouse might. For example, my bride, Maire Anne, and I are unlikely to use one of the fun vintage cars to go out to dinner if it’s 90 degrees out, she’s dressed to the nines, the car has no A/C, and we need to pick up a gallon of milk on the way home.

The whole A/C thing began for me when Maire Anne and I lived in Austin, Texas, for a few years in the mid-1980s. Austin isn’t Houston in terms of the humidity, but it was certainly much hotter than Boston, with temperatures reaching 90 degrees in May and staying there—with sojourns in the 100s—through September. I bought my first roundie BMW 2002, sorted it out, and was happy as a clam. But then I found a similar 2002 that had air conditioning, the prospect of which made Maire Anne very happy.

Maire Anne beams at my newly-purchased 2002 (front), which, unlike the last one (back), had air conditioning.
Maire Anne beams at my newly-purchased 2002 (front), which, unlike the last one (back), had air conditioning. Rob Siegel

Unfortunately, the air conditioning in the newly-purchased A/C-equipped 2002 didn’t work. I was becoming a very capable backyard mechanic, but I was used to problems that lended themselves to simple visual diagnosis—antifreeze streaming out of a water pump bearing, for example—and didn’t know the first thing about how to diagnose why an air conditioning system wasn’t working and figuring out which of the myriad of components distributed throughout the car needed to be replaced.

Fortunately, I worked with a fellow who had a lot of automotive A/C experience. He hooked up his manifold gauge set to my 2002 and diagnosed the problem as a stuck expansion valve. I ripped out the evaporator assembly from under the dash, opened it up, replaced the expansion valve, and reassembled the system. My friend then evacuated and recharged the system for me, and I had a cold car. I worked this way for about 15 years, paying someone to diagnose the cause of an A/C problem, replacing whatever part they told me was bad, then taking the car back in to be evacuated and recharged.

Then, about 20 years ago, I decided that I wanted to retrofit air conditioning into my pride and joy—my 1973 BMW 3.0CSi, which I’ve owned since 1986. Fortunately, the car was available new with A/C, so the correct interior pieces could be obtained. Unfortunately, even when these cars were new, vintage German cars were the poster children for anemic air conditioning (my colleague Mike Miller describes German A/C as “a hamster blowing over a snow cone”). So when you combine that with replacing the car’s original R12 refrigerant with the less-efficient R134a refrigerant that superseded it, the result is often disappointment.

The A/C retrofitted into my 1973 BMW 3.0CSi. Most people with vintage cars will be happiest in the long term if an original evaporator assembly and air-conditioned console can be sourced.
The A/C retrofitted into my 1973 BMW 3.0CSi. Most people with vintage cars will be happiest in the long term if an original evaporator assembly and air-conditioned console can be sourced. Rob Siegel

So I researched, read, and learned how to do it all myself, including diagnosis, evacuation, and recharge. Since the A/C retrofit in the 3.0CSi, I’ve resurrected or retrofitted A/C into six of my vintage BMWs. There is, in fact, a procedure when rejuvenating the A/C in a vintage car or installing an A/C system from scratch, which can maximize the likelihood that, once you’ve gone to all that work and expense, the system actually blows cold enough to be useful. These are the basic steps:

  • Replace the original upright piston-style compressor with a smaller, lighter, more efficient rotary-style compressor.
  • Replace the original serpentine-flow condenser with the largest modern parallel flow condenser that will fit in the nose of the car.
  • Install the largest auxiliary cooling fan that will fit on that condenser.
  • Resign yourself to the fact that, if you’re doing these things, you’re likely going to need to make all new A/C hoses. There are only four of them, so just suck it up and do it, or pay someone else to.
  • Anytime you open up an A/C system, you need to replace the receiver-drier.
  • As part of this updating process, replace as many of the original leak-prone flare fittings with modern O-ring fittings as you can.
  • If you’re resurrecting a system, remove the evaporator assembly, remove and replace the expansion valve, flush the evaporator core, lubricate the fan motor, reassemble, and pressure-test the assembly before you re-install it.
  • If you’re doing a from-scratch installation, and if the car was originally available with A/C, if you want the car’s interior to look stock, buy a console and evaporator assembly from a parts car. There may be aftermarket evaporator assemblies that fit under the dash, but the more valuable the car, the more you may regret using anything in the dash that does not look bone-stock.
  • Be certain that the internal refrigerant surfaces of any components you’re reusing are spotlessly clean.
  • Fill the compressor with the correct amount of ester oil, which can be used with both R12 and R134a. In contrast, PAG oil works only with R134a, so if you fill the system with it, you lock yourself into R134a unless you flush all the oil out of the system and refill it.
  • Pressure-test the system with nitrogen and verify that it maintains pressure.
  • Read on enthusiast forums about the experience others have had converting your car from R12 to R134a. If other folks who live in a climate similar to yours say “I’m using R134a and it blows cold,” try using it. But if the A/C has a tiny evaporator assembly and you live in a very hot climate, you may need to fall back to using good old-fashioned R12, which despite what you may have read is available and perfectly legal, provided you have an EPA 609 certification, which you can obtain by taking an online test. If you filled the system with ester oil, you can switch back to R12, as ester oil works with both R12 and R134a.

The choice of refrigerant can be crucial in a vintage car.
The choice of refrigerant can be crucial in a vintage car. Rob Siegel

If it sounds like I know this stuff pretty… uh… cold, I do. I wrote a new book, Just Needs a Recharge: The Hack Mechanic™ Guide to Vintage Air Conditioning, which should be coming out any day now. During the coming weeks, I’ll be writing columns on A/C theory, needed tools, the compressor, the evaporator and expansion valve / orifice tube, the condenser and auxiliary fan, pressure-testing and leak detection, evacuation, recharge, and troubleshooting. There will be more detail in the book, but I’ll give you a pretty good taste of it here.

After some teething issues with the retrofitted A/C in my 3.0CSi, I began driving the car first hundreds and then thousands of miles to attend vintage BMW events—another reason to have working A/C even though I live in relatively temperate Massachusetts. While driving home from one event and heading across western Pennsylvania, I hit a stretch where both the temperature and the humidity topped 90. I was tooling along in the 3.0, windows up, cool as a cucumber, living the dream, when I overtook a 2002tii driven by two friends. Both of the 2002’s front windows were rolled down, and I could literally see the streams of sweat being ripped from the foreheads of the driver and passenger and aerosolized by the passing wind. I couldn’t help think, “How’s that R75/2 workin’ for you now?” I say this not because I am a bad person and enjoy gloating in the misery of others, but because a) you have to admit that it’s funny, and b) it shows how A/C rejuvenation or retrofit is one of those repairs where, although it’s time-consuming and is not inexpensive, the enjoyment and comfort of a cold car can be absolutely priceless.

So watch this column for A/C info, and look for the book on Amazon. It’s about to get chilly.


Rob Siegel has been writing the column The Hack Mechanic™ for BMW CCA Roundel Magazine for 30 years. His new book, Ran When Parked: How I Road-Tripped a Decade-Dead BMW 2002tii a Thousand Miles Back Home, and How You Can, Too, is available here on Amazon. In addition, he is the author of Memoirs of a Hack Mechanic and The Hack MechanicGuide to European Automotive Electrical Systems. Both are available from Bentley Publishers and Amazon. Or you can order personally inscribed copies through Rob’s website:

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