Last week, the dynamic of “it’ll never be easier than right now” got the better of me, and I delayed the evaporator installation in order to remove, rebuild, and reinstall the heater box. (Actually, it wasn’t “it’ll never be easier than right now.” It was “all the foam has worn off these flaps and it’ll leak more hot air than [fill in your least-favorite politician].”)

But this week, the evaporator assembly finally went in.

As I said a few weeks ago, if you divide up the daunting a/c retrofit process into the manageable-sized projects of compressor and bracket, condenser and fan, evaporator assembly, hoses, wiring, and leak-testing and recharge, then dealing with the evaporator assembly is probably the biggest single job. Since I’ve already covered rebuilding it (disassembly, flushing, replacing the expansion valve), and the nerve-wracking process of drilling holes in the firewall for the refrigerant hoses, you’d think that at this point, installing the assembly would simply involve sitting it on the transmission tunnel.

And you would be wrong.

On a 2002, it is almost that simple. A 2002’s evaporator assembly has the electrical controls (temperature and fan speed, where zero fan speed shuts the a/c off) dangling right off it, and the output vent is right there on the front of the box. There’s no ventilation interface to the car, and there’s very little electrical interface. There is a bracket that you’re supposed to screw into the tunnel, but it’s often missing, or the attachment points on the box are often cracked. As long as the evaporator drain is over the hole in the transmission hump, you almost can just set it on the tunnel and hook up the refrigerant lines. Any other clearance and alignment issues are virtually nonexistent.

On an E3 or an E9 (3.0CS or Bavaria), it’s a little more complicated. Electrically, the switches still dangle from the evaporator assembly and mount to a faceplate, but the assembly doesn’t have its own air-output vent like a 2002. Instead, the assembly is open at the top, and uses what’s listed in RealOEM as the “intermediate piece,” sort of like a box of Kleenex turned on its side and open at the top and bottom, that connects it to the dashboard vents. Therefore, servicing the evaporator assembly on these cars involves removing and installing the intermediate piece. It’s 45-year-old plastic, and it cracks into splinters if you even look at it too hard. For this reason, I try not to pull the evaporator assembly out of E3s or E9s unless there is incontrovertible evidence of contamination or a failed component inside.

I didn’t really know what to expect with the Shark. It’s a ’79, making it an early E12-based car, so by modern standards it’s pretty primitive. There’s still a separate evaporator assembly and heater box. It’s not like a modern car, where there’s a blend door mixing heated and cooled air; they’re still two completely separate systems. Like the E3 and E9, the evaporator assembly is open at the top, so clearly some sort of intermediate piece was required.

I was incredibly fortunate that the gentleman from whom I purchased the evaporator assembly sold me not only the assembly, but everything it touched on the inside of the Euro ’79 635CSi that he was parting out. This included not only the intermediate piece, but the entire heater box. Thus, I thought I would be able to see how the evaporator assembly, the intermediate piece, and the heater box went together before I even put them in the car.

But I couldn’t figure it out.

It turned out that, on the underside of the dashboard ventilation ductwork in my car, there was a block-off cover with guitar-case-like latches that snapped it in place. I needed to unsnap it and substitute the intermediate piece.

I replaced the deteriorated foam around the openings of the intermediate piece to reduce the chance that the precious chilled air from the evaporator assembly would leak out before blowing in my face, and then installed the piece.

Before installing the evaporator assembly, I needed to mount the bracket that holds it on the transmission hump and drill the drain hole. Fortunately, there were cut-outs in the sound-deadening material where the feet of the bracket had to go.

Unfortunately, once I pulled the cut-outs away, there was nearly an inch of uncertainty in the bracket position. I shrugged, put the bracket about in the middle of the cutouts, eyeballed it so it wasn’t cocked side to the side, and marked and drilled the holes for the screws holding it in place. I then marked the hole for the drain and drilled a pilot hole. I didn’t have a hole saw that size, but by using larger drill bits, then switching to a Dremel tool with a routing bit, I was able to enlarge the hole to the size needed to receive the drain tube.

I attached the bracket, but left the screws loose so it had some play on the transmission hump. I then test-fitted the evaporator assembly onto the bracket, sliding it in place at an angle, then up and into the intermediate piece. I looked up top to make sure that the assembly was seating correctly on the intermediate piece and not twisting it, and looked beneath the assembly to verify that the drain tube went into the hole that I’d drilled for it. I appeared to have gotten the bracket location about right, so I took the assembly back out, tightened the bracket in place, then reinstalled the assembly.

With all holes drilled and the evaporator assembly finally secured on the tunnel—hopefully for good—I breathed a sigh of relief. I felt like I’d scaled the big peak, and it would all be easy going from there to the finish line.

Then I noticed something.

Unlike the other cars in which I’d done this process, the evaporator assembly I’d just installed had no controls hanging off it. No temperature control. No fan speed control. Nothing! How do you control it? How do you even turn the air-conditioning on and off? What was I missing, both in parts and in understanding?

I looked in the parts box the seller had sent me, and saw that there was a heater-control panel. I’d looked at it once before, but assumed that, like the spare heater box, it had just been thrown in there for completeness and I didn’t need it. This time I examined it more closely; there was no air-conditioning button on it, like there is in an E30 or an E28. From the front, it looked just like the one that was in the car, except that it had a really cheesy-looking but original digital clock, whereas the one in the car had an analog clock, and it had blue-and-red swoopy symbols around the temperature knob, whereas the one in the car was all black.

But then I turned the heater control panel over and saw that on the back, it had a box with a metal thermocouple probe that clearly was supposed to snake inside the evaporator assembly. This obviously was the a/c temperature sensor and switch. There were also two relays on the back of the panel. And, on close examination, I saw that there was a microswitch on the temperature knob that was tripped closed when the knob was turned into the cold (blue) region.

This wasn’t a heater-control panel: It was a climate-control panel.

It was clear that I was mistaken in thinking that the heat and a/c in the Shark were completely separate systems. Instead, the compressor’s turn-on and the evaporator’s temperature and fan speed were controlled by this panel. I’d have to pull out my existing panel—which actually was a heater-control panel—and install this one.

It actually wasn’t too bad. I yanked the old one out and test-fitted the a/c-equipped one, plugging it into the car’s wiring harness and mating its additional connector to the one coming out of the evaporator assembly. Then I re-connected the Shark’s battery for the first time in months.

To my delight, the panel did what it was supposed to.

With the temperature knob in the red, the fan-speed control governed the fan in the heater box, but when you turned the knob into the blue range, the relay switched fan-speed control to the fan in the evaporator assembly. Cool!

Unfortunately, I knew instantly that both the digital clock and the red-and-blue swoops on the temperature knob would bother me until the end of my days, so I pulled the panel back out, put both panels on the table, and set myself upon the task of performing the Frankenstein’s monster transference. Out came both clocks. I found that the connectors on the digital and analog clocks were different, but, as is so often the case, I was not the first person to encounter this problem. I found a post on about chopping the multi-pin connector off the cable for the digital clock and crimping on the spade connectors needed to adapt an analog clock. I thought that I could get rid of the colored swoops by swapping the faceplates, but it looked like the mounting for the microswitch that turns on the compressor was integral with the faceplate, so, at least for now, I let that one go. I test-fitted the analog-clock-equipped panel into the Shark and checked its functionality.

The clock worked, but to my intense disappointment, the loosely-installed panel no longer switched on the evaporator fan.

I assumed that I’d broken something in my clock-swapping. I wired the fan directly to the battery to make sure that it still worked. I verified that there was 12-volt power on a number of the pins in the connector from the new faceplate. I connected one of those hot pins via a jumper wire to the evaporator connector, and the fan turned on. But when I mated both halves of the connectors, I still got nothing. This went on for nearly 90 minutes, until I finally realized that even though it’s a keyed connector, it was still possible to plug it in backwards—and I had done just that. I’m lucky I didn’t fry something.

With the connector plugged in correctly, the evaporator fan returned to life.

I permanently installed the panel, and with that, the installation of the evaporator assembly and its controls was finally complete. Whew! Now it really should be an easy downhill to project completion (he says, clearly tempting the Air-Conditioning Minions of The Automotive Powers That Be).

There is still the question of exactly how the compressor gets switched on—what the connection is from that microswitch on the rotary temperature dial to the compressor. I figured it out, but I’ll leave that for when I cover the subject of the final electrical connections. We’re getting close.

Just in time for winter, true—but I prefer to think of it as ready for spring.—Rob Siegel

Rob’s new book, Ran When Parked: How I Resurrected a Decade-Dead 1972 BMW 2002tii and Road-Tripped it a Thousand Miles Back Home, and How You Can, Too, is now available on Amazon. Or you can order personally inscribed copies through Rob’s website: