Last week, the evaporator assembly finally went into the ’79 Euro 635CSi. Together with the compressor and condenser, this meant that the Big Three pieces of air-conditioning hardware were installed.

The next step is installation of the hoses that connect them.

If, as I said last week, dealing with the condenser is my least favorite part of a/c rejuvenation or retrofit, then fabricating and installing the hoses is my most favorite. In a from-scratch a/c retrofit, you make fabricate and install all new hoses; in a rejuvenation, you almost always wind up doing so as well—at least I do. Here’s why.

Although there was a crossover period in the 1980s where some Freon-based a/c systems (such as those on E30s) had components with O-ring fittings, most a/c systems that originally used Freon had flare fittings on all of the components. Make no mistake, O-ring fittings are far superior; they’re much less leak-prone than flare fittings. Thus, when you’re in the process of rejuvenating or upgrading a system and you change from an old, large, inefficient piston-based compressor to a new compact rotary-style unit, and from a serpentine-flow condenser to a more efficient parallel-flow one, you’re also changing from old components that have leak-prone flare fittings to modern ones that have better-sealing O-ring fittings.

Unfortunately, your original hoses still have flare fittings on them.

Sometimes you may get lucky and be able to chop the old flare fitting off a hose and crimp an O-ring fitting on the end, but that’s false economy. You’re already doing all this work; you should ensure a leak-free system by installing all-new a/c hoses. There are only four of them at most anyway.

In addition, any time you open up an a/c system, you should replace the receiver/drier. So all this work gives you an opportunity to replace it with a new drier that has O-ring fittings instead of flare fittings. Unfortunately, if you have a 1970s-era car, its old evaporator likely has female flare fittings—at least it does on 2002s, E3s, E9s, and E12-based E24s like mine—and there’s no getting around it, because they’re integral with the evaporator’s hard lines. If you want, you can install flare-to-O-ring adapters, and I’ve done that, but the fittings on the evaporator tubes themselves are still flares. So the likely path is O-rings on everything except the evaporator fittings. Got it? Good.

If you have to pay someone to make hoses, it can get pricey, but the hoses and fittings themselves are cheap. They can be bought from any number of places, including NAPA and websites such as, but I use a guy whose eBay handle is johnjoysl and whose store name is Mr Fomoco Motocraft. Hose is typically about three bucks a foot, and fittings typically cost between three and ten dollars each. So in materials, you’re talking maybe twenty to thirty bucks a hose.

All you need in order to turn these parts into a ready-to-install hose is a crimping tool. If you plan to do this kind of a/c work more than once, you should just buy the tool—and THE tool is the Mastercool 71500 Hydra-Krimp, a handheld hydraulic device that crimps beadlock fittings onto hoses. It comes with a set of swappable dies for the different-size fittings and hoses. Unfortunately, its list price is big money—over $600.

You can buy its smaller companion, the Mastercool 71550, for closer to $150 instead. The 71550 is just the crimping portion without the hydraulic hand-held assembly. This requires you to hold the tool in a bench vise and tighten the crimping jaws down onto the fitting with a wrench. It’s better than nothing, but unfortunately it removes a big part of the utility of the 71500, which is that you can crimp the fitting on one end on a hose, install that end in the car, and then, in situ, measure the exact length the hose needs to be to reach the other end, cut it, and crimp the other end on it right there in the car.

Due to the double-edged sword of Far East manufacturing, Chinese-made knockoffs of the 71500 Hydra-Krimp are now available on eBay for about $250, aping the same form factor and even using the same color crimping dies as the Mastercool. I am not making a recommendation either way. I have a used Mastercool 71500 that I bought years back on eBay; I love owning and using it.

As you’re preparing to make hoses, or to have them made, it’s best to be organized and make a table of the fittings on each component, and from there determine the fittings needed for each hose. Geek alert: I do this in Excel. On an a/c retrofit or upgrade on most vintage European cars, this is what you will find:

New Rotary-Style Compressor:
Input (suction side): #10 O-ring
Output (discharge side): #8 O-ring
New Parallel Flow Condenser:
Input: #8 O-ring
Output: #6 O-ring
New Receiver-Drier:
Input: #6 O-ring
Output: #6 O-ring
Original Evaporator:
Input: #6 flare (you’ll see below that for the shark, I have this wrong)
Output: #10 flare


Now that you’ve listed the fittings component by component, you need to know how these components are connected. Every automotive a/c system I’m aware of is plumbed as shown below. The compressor discharge hose goes to the condenser inlet. The condenser discharge hose goes to the drier inlet. The drier discharge hose goes to the evaporator inlet. The evaporator discharge hose goes to the compressor inlet (the suction side).

Thus, you need to fabricate four hoses. So rather than being component-centric like the list above, you need to be hose-centric. Double-geek alert: I actually do via in a linked table in Excel to make sure I’m not screwing things up.

Hose #1: Compressor output (discharge) to condenser input
Input: #8 O-ring
Output: #8 O-ring
Hose #2: Condenser output to drier inlet
Input: #6 O-ring
Output: #6 O-ring
Hose #3: Drier outlet to evaporator input
Input: #6 O-ring
Output: #6 male flare (you’ll see below that, for the shark, I have this wrong)
Hose #4: Evaporator output to compressor input (suction)
Input: #10 male flare
Output: #10 O-ring

You’ll notice that in the above list, the input and output fittings on each hose are the same size. Although the fittings do have actual sizes (#6 is 3/8-inch, #8 is ½-inch, #10 is 5/8-inch), they and the hose are usually simply referred to by the fitting number. Most of the time, you use (taking the last hose as an example) a #10 hose with #10 fittings at both ends. There are also what are known as step-up and step-down fittings for the rare occurrences where the sizes of the needed fittings are asymmetrical.

Before ordering fittings, you need to suss out what angles you need for each. Beadlock fittings come in straight, 45-degree, and 90-degree versions. On the condenser, you usually want 90-degree fittings, often configured as short drop fittings in order to maximize clearance (I described these in the installment on the condenser). The fittings for the drier are usually straight or 45-degree fittings; compressor fittings are usually 45 or 90 degrees so the hoses can curve away from the engine. Judge as best as you can by eyeballing each component, and when in doubt, simply order any and all that you think might work. They’re cheap.

You also need to deal with the issue of charging ports—the places where the gauge set attaches, enabling you to leak-test, evacuate, and charge the system. You can splice charging ports into the hoses on the low- and high-pressure sides, or use compressor-hose fittings that have charging ports built in. I tried that, but found that there wasn’t sufficient clearance to use them; in the photo below, you can see the top of the charging port nearly hitting the block.

Because of this, I elected to simply use the charging ports already in place on the back of the compressor. The downside is that you need to put an adapter on one of them, and they’re quite inconvenient to reach—you pretty much have to jack up the car and connect the gauge set from underneath—but once the system is leak-tested and recharged, you don’t need to access them again unless something goes wrong.

I’ve lumped the receiver-drier into this installment on hoses because it’s a fairly trivial component. The drier is basically just a canister with desiccant in it that absorbs any moisture in the system; virtually any drier will work. They come in a variety of lengths and diameters. It’s just a matter of figuring out where to mount it. The drier needs to be in line between the condenser output and the evaporator input. For practical reasons, it is usually somewhere on the right-hand inner fender wall. It should be kept away from the exhaust manifold, so it is usually either up high in front of the firewall, which is the factory location on an early E12-based shark like mine, or down low closer to the nose, which is where it is on a later E28-based shark.

On cars like E3s, E9s, and E24s, there are hard-metal a/c evaporator lines running through the firewall. On my E24, as originally configured, the drier’s outlet port attaches directly to the hard-metal evaporator input line. This means that there is no “hose #3.” Generally speaking, fewer hoses is a good thing, since it means fewer fittings that can leak. But when you’re retrofitting or rejuvenating, this creates a tradeoff: Do you stay with an old-style drier with flare fittings and attach it directly to the evaporator input line, or do you convert to O-ring fittings, even though that may necessitate another hose? I did what I often do and ordered parts to try it both ways. Driers are cheap, about fifteen bucks. I ordered one with two flare fittings and another with two O-rings. Both of the ones I ordered were short, about six inches tall, leaving room under the drier for the other hard line to pass beneath it. I also ordered a set of flare-to-O-ring adapters.

When your hoses and fittings arrive, before you begin fabrication, it’s important to test-fit every fitting onto the place it’s supposed to go. Sometimes you don’t have the clearance you thought you did, as was the case with the charging ports on my compressor hoses. And sometimes you simply get a bad fitting, with threads that don’t mesh with those on the component. Best to find these things out before you crimp the fittings onto hoses.

I fabricated the hoses in the order listed above. I first crimped on the short-drop fitting for the condenser, then test-fitted it in place.

I passed the hose through the nose and into the engine compartment, threaded the other fitting onto the compressor, cut the hose to length, inserted it into the fitting, marked both so that I could crimp the fitting on in the orientation most favorable to the bend in the hose, then removed the fitting from the compressor and crimped it in place on the hose.

The next hose ran from the bottom of the condenser to the drier. I crimped on the short-drop fitting for the condenser and ran the hose through the nose, and then was faced with the question of which one of the driers I’d bought to connect it to, and thus where to mount it and which fitting to crimp onto the other end. The best location for the drier really did seem to be the original location, up high near the firewall, directly connected to the evaporator hard line. I investigated the O-ring drier first. I tried to use the flare-to-O-ring adapter, but was immediately confused; the adapter, it seemed, didn’t allow the threads on the nut on the hard line to mate with the fitting on the drier. Okay, I thought, too bad; guess I’ll have to use the drier with the flare fittings. But when I tried it, I had the same problem—the nut on the hard line wasn’t the same size as the threads on the drier’s flare fitting.

My brain took a moment to process the fact that the problem had nothing to do with adapters. The problem was that the evaporator input hard line wasn’t a #6, which is what the drier fittings are; it was a #8. Neither of the driers I’d bought would fit. I’d either need to order step-down fittings and make a hose and mount the drier somewhere else, or get another drier that had a #8 output port.

Looking online, I was able to find both flare and O-ring driers that had #8 fittings. One of them, a Mercedes replacement drier, even had a #6 flare input and a #8 flare output, so it wouldn’t even require any step-up or step-down fittings. When I looked at this drier, I realized that I had one sitting in my basement, something I’d bought when I was entertaining options for a 2002 installation years back. I didn’t use it back then for a number of reasons, including the fact that it had an integrated bracket that was mounted at the wrong angle. I unearthed the drier, cut the bracket off, and test-fitted it. It appeared to solve my problem. On the plus side, I had it right there, I didn’t need to order anything and wait for it to arrive, it bolted directly up to the evaporator input line with no adapters, I already had a #6 flare fitting to mate to the input side, and it looked nearly stock. On the negative side, that meant having one more flare fitting than I would’ve had if I switched to an O-ring unit. But I hated the idea of having to wait another three days for another drier, so I decided to use it.

When I made the final hose that runs from the evaporator output into the compressor suction line, hose fabrication was complete. It was all done in an evening. Most enjoyable.

I then attached the fittings for real. This involves coating all threads and O-rings with Nylog sealant (or “fitting snot,” as it is affectionately called), and using copper flare washers on all of the flare fittings. I had a stash of these somewhere, but could not find them. I had the fellow at the eBay store I mentioned above overnight me a set.

I torqued everything down. With O-ring fittings, the O-ring provides the sealing, so you don’t need to tighten them down with a dying strain. With flare fittings, though, it’s the metal-to-metal surface that’s doing the sealing, and you sometimes need to really crank down on them to get the sealing faces mated properly.

I examined my handiwork, and deemed that it was good.

I then prepared to leak-test the system. But in true cliff-hanger fashion, I will leave that for the next installment.—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: