Resurrecting the FrankenThirty’s Air Conditioning

About ten years ago, I bought a 1987 BMW E30 325is that had a seized compressor. I resurrected its air conditioning by finding a used compressor, flushing the system out, and recharging it with good old-fashioned R12. My logic was that, as I explain in my book Just Needs a Recharge: The Hack Mechanic Guide to Vintage Air Conditioning, since R134a doesn’t cool as well as R12, when you convert a car from R12 to R134a, if you want it to blow cold, you generally have to replace the original serpentine-flow condenser with the largest modern parallel-flow unit that’ll fit in the nose, as well as a big condenser fan, both of which require adaptation. By sticking with R12 (which is not illegal, though discharging it into the environment is, as it is with any refrigerant), you avoid having to do that extra work. You do, however, create potential problems up the road, as most shops these days won’t work with R12.

That strategy worked perfectly ten years ago, so when I began resurrecting the A/C in my current 1988 BMW E30 325is (a.k.a. the FrankenThirty) last fall, I thought I’d try the same approach. An additional reason was that this car has a salvage title and has the nose from a pre-facelift 1987 car grafted onto a facelifted 1988 body. This kills any headroom in the car’s value, and makes me hesitant to apply “do it once, do it all, do it right” solutions to problems. Fortunately, the FrankenThirty’s compressor wasn’t seized—it was just contaminated with deteriorated foam. Rebuilding it, flushing the lines, and charging with R12 made sense to me as a low-cost approach.

Unfortunately, if the goal is working air conditioning, you have to play the hand the car deals you and fix what needs fixing. On the FrankenThirty, this wound up involving most of the system. On one hand, this wasn’t really surprising—in my book, I say that if you’re looking at resurrecting a long-dead a/c system in a car and think that you’re going to get out of it without replacing every single a/c component under the hood and possibly the ones under the dash, you’re deluding yourself. On the other hand, with the E30 two generations newer than the 1970s-era BMWs whose A/C systems I usually wrench on, I thought that “newer” would translate into “less needy.” I was wrong.

Let me back up a step. When I talk about “vintage air conditioning,” what I mean is a system that A: originally had R12 in it and thus if converted to R134a needs improvement in order to blow cold, B: has heat and a/c in separate boxes and doesn’t have “climate control” where they’re blended, and C: doesn’t have any “block-style” A/C fittings that are unique to the car. The BMW E30 sold from 1984 through 1991 straddles this line. It was originally an R12 car with a serpentine-flow condenser, but it has a single box that houses both the heater core and the A/C evaporator core as well as a modern rotary-style compressor. It doesn’t have unique block-style A/C fittings, but it does have aluminum A/C pipes that hug the right inner fender and run into the passenger compartment.

Also, let me get on my soapbox for a moment. Some folks say that air conditioning just complicates an old car and makes it heavier, then gleefully talk about ripping it all out and driving windows-down American Graffiti-style with their left bicep showing. The expression for this, riffing on the whole R12-or-R134a-refrigerant-thing, is sometimes referred to as “R75/2” (75 mph, two windows down). I am so not an R75/2 person. Even though Massachusetts is temperate as compared with the south or southwest, I love having working A/C in my cars—my daily drivers as well as my vintage rides. For pleasure drives or an evening out with my wife, if it’s 90 degrees out, I’m far more likely to take one of the vintage cars if it’s air-conditioned. Thus, I view working A/C as a way to extend my use and enjoyment of a car in what is already a short driving season. And when I do road trips, I find the wind noise from windows-down driving very fatiguing. I attend a show called The Vintage in Asheville, North Carolina, every year around Memorial Day. It’s a 2000-mile round trip. It typically gets hot and humid as soon as I hit Pennsylvania. I vividly remember driving my air-conditioned 1973 BMW 3.0CSi ten years back, windows up, cool as a cucumber, when I passed two guys I know in a BMW 2002tii. Both their windows were down, and I could literally see the sweat flinging off them. I thought, “How’s that R75/2 workin’ for you now?”

I actually began the FrankenThirty’s A/C work shortly after I bought the car last August and de-moused the seriously-contaminated heater box. As I said, the E30 has a single box containing both the heater core and the evaporator core. Plus, unlike the older BMWs I’m used to where you have to remove the evaporator assembly and open it up in order to access the evaporator core and the expansion valve, in a nice bit of design, both cores can be slid out from the side without actually removing the heater box from the car. This allowed me to clean the box in situ.

Unfortunately, the combination of the density of the fins on the evaporator core and the degree of mouse contamination made it so I could never get the smell out despite multiple pressure-washings and soakings in enzyme-based cleaner. I replaced it with a good used core and installed a new expansion valve on it.

The A/C work continued over the winter. A big hiccup came when I damaged the compressor while rebuilding it. Fortunately, I was able to find a never-used, professionally rebuilt compressor for a hundred bucks. It came filled with PAG oil, as is customarily used when retrofitting R134a, but that’s incompatible with R12. Draining it and refilling it with mineral or ester oil for R12 isn’t a big deal, but I thought I’d first see what other problems the system had. Blowing out the system with compressed air (a precursor to flushing with mineral spirits) produced an alarming amount of rust, likely coming from the original serpentine-flow condenser. I knew that if I were advising anyone else, I’d say, “Yeah, you’d be an idiot not to replace that.”

So down the rabbit hole I went. I wire-brushed the portions of the metal tubing that I could reach, and looked at replacing the condenser. Fortunately, to my delight, I found that the commercial off-the-shelf replacement condenser is actually a drop-in parallel-flow condenser (no adaptation necessary) that can be had for about a hundred bucks shipped. Having resurrected A/C in a dozen vintage BMWs, I’ve never seen this; I’ve always had to measure, fit, and custom-mount one myself. I credit its availability to the large number of BMW E30s sold and still on the road. I tested the car’s original condenser cooling fan, made sure it still worked, mounted it on the new condenser, and installed it.

While replacing the condenser, I inspected the hoses that plumbed it. Although I found no direct signs of leakage, one of the hoses had a gash, the other had a bulge next to the crimp. The gashed one was a simple rubber hose—the only one in the A/C system—that I easily fabricated myself. The other was a hybrid rubber-and-bent-aluminum hose that’s unique to the car. Fortunately, it was only about $45.

While pressure-testing the system, I had persistent problems getting the large suction fitting on the compressor to seal. O-ring fittings are designed so that when you feel the metal-on-metal contact when the male fitting bottoms out inside the female one, the o-ring is properly squeezed; you shouldn’t need to have to judge tightness. And yet, for some reason, this fitting would cut its o-ring if I snugged it all the way down, and leak if I didn’t. I didn’t see anything wrong with the male end of the fitting, but I replaced the hose anyway. Fortunately, the $61 order solved the problem, and the system passed its nitrogen pressure test.

Then I began testing the electricals. On a vintage car, the A/C electrical system is trivial. The blower fan switch typically triggers the compressor and sends voltage to a relay that turns on the condenser fan. Although the E30 technically doesn’t have climate control, it does have its A/C coupled with the car’s heating and engine cooling systems in a number of ways. There’s a switch inside the temperature control dial that blocks coolant flow to the heater core if the A/C is on, and depending on the year of the car, there’s an anti-icing switch on the vent sliders that won’t turn on the A/C unless a certain amount of air is passing over the evaporator core (yeah, you wish an R134a-converted car gets cold enough to freeze the evap core). Neither of these was connected; the console needed to be removed to access both, and the latter one was broken. I bypassed it. That, combined with the fact that the compressor wire had clearly been cut, made me realize that it was likely that this car’s A/C had never been operational after its salvage event in 1992. With these fixed and the pressure sensors on the receiver-drier bypassed, I was able to get 12 volts on the compressor wire when I turned the A/C on.

That left only the condenser fan. As on many cars, the E30’s two-speed fan does double-duty on the condenser and as an auxiliary radiator cooling fan, so it’s triggered not only by the A/C-on switch but also by the temperature sensor on the radiator. I had tested the car’s original condenser fan before reinstalling it, but had missed testing its resistor, which turned out to be bad. I bypassed it, but still the fan wouldn’t turn on along with the A/C. The problem turned out to be due to a grounding issue in the fan’s low-speed relay.

With both the compressor and fan turning on, I could finally evacuate and recharge the system. Cars that originally had R12 have threaded A/C service ports that look like Schrader tire valves. In contrast, cars sold after 1992 that are charged with R134a have threadless snap-on quick-connect-style fittings. When you convert from R134a, you’re supposed to install R12-to-R134a adapters. Although the original reason was to reduce the possibility of an A/C repair shop cross-contaminating its recovery equipment, you should use the conversion fittings because once the system is charged, their quick-disconnect capability allows you to remove them without losing a drop of coolant. In contrast, when you unscrew the hoses from the old-style R12 fittings, it looks like you dropped Mentos in a Coke bottle. Unfortunately, the high-side fitting on the E30’s discharge line comes so close to the hood mechanism that I wasn’t able to get an adapter on it and close the hood.

So, after leak-testing and evacuating the system, I could finally charge it. Charging a system that had R12 in it with R134a isn’t an exact science, so looking on user forums for a fill guideline is always helpful. The consensus seemed to be to charge with 28 to 32 ounces of R134a. In a perfect world, you’d buy two 16-oz cans, but for reasons unknown, R134a seems to only be available in 12-oz cans. I shot in one can, smiled when I engaged the compressor and the readings on the manifold gauge set verified that the rebuilt compressor was actually working (the low-pressure gauge dropped and the high-pressure readings increased), saw the temperature probe I’d put in the vents slowly drop, then shot in the second can and took the car for a drive.

And?

37-degree vent temps, baby! Of course, it was probably only 65 degrees out, so that’s not quite as impressive as it sounds, but still: For probably the first time since the car’s salvage event in 1992, the FrankenThirty has working A/C.

In the end, I replaced every major component except the condenser fan and the hard metal lines. The total parts bill for all this crept up, but it wasn’t bad—about $500. If you had to pay someone for this degree of A/C resurrection, it’d cost thousands. And it’d never be worth it on a value-capped car like this one. But I have to tell you—of all the DIY work I do, A/C resurrection has to be the most satisfying. So much of resurrecting a long-dead car is just getting things to function—where fuel systems deliver fuel, brakes brake, charging systems charge, etc. And, after all that work, it’s not like you jump in the car and smile every time it does those basic things. But to take a car and make it cool and comfortable to drive long distances, man, turning on the air and feeling it blow cold never gets old.

Really, if you think about it, when you prepare a car to take on a road trip, you pay a lot of attention to the cooling system to make sure the engine doesn’t overheat. When you resurrect an A/C system, you’re making sure that you don’t overheat.

In two weeks, I’ll be driving the FrankenThirty down to The Vintage in Asheville. If I see you driving windows down and sweat wringing from your brow like a mop, I’ll really try to be the better man and not yell “How’s that R75/2 workin’ for you now?”

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Rob’s latest book, The Best Of The Hack Mechanic™: 35 years of hacks, kluges, and assorted automotive mayhem, is available on Amazon here. His other seven books are available here on Amazon, or you can order personally inscribed copies from Rob’s website, www.robsiegel.com.