Upgrading to a Parallel Flow Condenser

thehackmechanic

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(This just ran as my weekly Roundel Online piece (https://www.bmwcca.org/roundel/conditioning-coupe-part-701-700), but obviously it belongs here too, so I'll just copy and paste it in. It's over the 10k character limit, so I've broken it into two.)

It’s hard for me to believe that it’s been 18 years since my series of columns entitled “Conditioning the Coupe (part XX of 700)” ran in Roundel. In them, I described the from-scratch retrofit of air conditioning into my 1973 3.0CSi. I’d done a/c repair before, but this was much more involved. I worked with a vendor who advised that I go with an R134a system since Freon (R12) had already been on the outs since the early 1990s and its long-term availability was questionable. To maximize the system’s performance, we took the extraordinary step of having a custom evaporator core fabricated that was the same size as the original core but had twice the number of passes of the cooling tubes through it. I found an original E9 evaporator assembly and the all-important plastic duct connecting it to the vents in the center console. The vender sold me the custom evaporator core, a rotary compressor and bracket for the M30 engine, a condenser, a receiver-drier, and a few other small parts. I paid someone to fabricate the hoses, and paid someone else multiple times to pressure-test the system, locate leaks, evacuate it, and recharge it.

After some initial teething pains, the system has remained functional for all these years. However, although I love having an air-conditioned coupe on long trips to The Vintage and other shows, the truth is that the system’s performance has been adequate but not great. In contrast with Freon-based systems which you turn on and they immediately blow cold, R134a conversions often take a while to spit cold air at you, and quite a bit longer to actually chill the interior of the car. When you combine that with a hot car that’s been sitting in the sun, the results can be disappointing. Even once the E9’s interior was cooled off, the car’s a/c would get overwhelmed on the stretches I’d routinely hit on the way to The Vintage where the temperature was 95 degree and the humidity 90%.

Over the years, I took a number of steps to mitigate the intrusion of heat into the cabin. I re-lined the foam on the heater box flaps to block off hot outside air, tinted the windows, and installed a valve to stop the flow of antifreeze to the heater core, which, unlike in a 2002, is always plumbed with hot antifreeze; the heater control lever merely opens up a flap to direct that heat from the heater box into the cabin. These things made some difference, but the E9’s a/c has never been bone-chilling cold.

Fast-forward to now. I know a lot more than I did then. I now do all of my own a/c work, including hose fabrication, leak-testing, evacuation, and recharging. My next book may well be The Hack Mechanic Guide to Vintage Air Conditioning. I know that, as cool as my custom double-pass evaporator core is, it probably wasn’t necessary, as evaporator performance usually isn’t the limiting factor of a/c performance—condenser performance usually is. I know that the type of serpentine flow condenser that’s original to any pre-1990s car and that was part of the retrofit into the E9 18 years ago is now obsolete, and that any a/c retrofit or rejuvenation should include a modern parallel-flow condenser. Rather than having a single serpentine tube snaking through it, a parallel flow condenser utilizes dozens of tubes acting in parallel to maximize the transfer of heat, thus increasing thermal efficiency, and with it, cooling. I know that the advice now is that, if you’re going to run R134a in a system originally made for Freon, if you don’t also upgrade to a parallel flow condenser, you’ll likely be disappointed. And I know that the reported death of Freon was exaggerated. It is still available, though it is increasingly difficult to find commercial shops who will work with it.

With this knowledge, I’ve actually taken things a step further. Both my ‘72tii and my Bavaria, whose a/c systems I’d rejuvenated by installing the biggest parallel-flow condenser that’d fit in the nose, installing the biggest fan that’d fit on the condenser, replacing the ancient upright piston compressor with a modern rotary one, are charged up with good old fashioned Freon, and get cold enough to hang sides of beef inside. You want a recipe for a cold car? It’s right there.

In addition to the E9 being equipped with a now-obsolete serpentine flow condenser, I made a mistake when I installed the condenser in 1999. When I went to get the hoses made, the fabricator (Ed Ellis, from “Ellis the Rim Man” on Comm Ave for you old-school Bostonians) discovered that I’d accidentally mounted the condenser upside down, with the #6 fitting at the top and the #8 fitting at the bottom. I should’ve just gone home pulled it out, and re-mounted it the correct way, but I had an appointment, I was there, and I wanted to get the hoses made. Fortunately, Mr. Ellis was able to make hoses with step-up and step-down fittings. He said it probably was a non-issue, but I’ve always wondered if it was one of the factors limiting performance.

So, for 18 years, the cooling in the E9 hasn’t been great, and I’ve second-guessed the use of R134a, especially since the tii and the Bavaria, which both run Freon, and which I rejuvenated after the E9, perform so well. For all these reasons, I’ve been itching for a reason to yank that serpentine flow condenser out of the E9, replace it with a modern parallel-flow unit (installed right-side up :^), evacuate the system of R134, charge it up with Freon, and write the wrong I did 18 years ago.

After I attended The Vintage in 2013, I thought I had my chance. You may recall my story of The Great Drenching Event, where I explained how I hit a solid 500 miles of torrential rain on the way to Winston-Salem. During the deluge, I saw something skitter off the back of a truck and then heard an alarming smack in the nose of the E9. When I stopped, I found that a clevis pin and chain had smashed through the E9’s front grille. The pin itself, a bit larger than a lipstick tube, had impaled the condenser. Miraculously, it embedded itself between two passes of the serpentine tube without puncturing it. But it did get me thinking about planning the condenser’s replacement.

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Oddly enough, it was the E9’s sister car, the ’72 Bavaria, that was ultimately responsible for the E9’s finally receiving its parallel flow condenser. When I bought the Bavaria a few years back, its a/c wasn’t working, so I embarked on my standard resurrection process that’s all but guaranteed to result in a cold car (big condenser and fan, rotary compressor, all new hoses, Freon). As part of this process, you need to identify the biggest condenser that’ll fit in the nose. It’s clear from the photo below that the E9’s 18 year-old 16"x20" serpentine flow condenser fit with gobs of room to spare, so in addition to going parallel, I wanted to go up in size.

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You can look on enthusiast forums and see if there’s an agreed-on maximum condenser size for your model, but Bavaria forums aren’t as active as, say, 2002 forums, so I measured for myself and bought a 16"x22" condenser. As is often the case, though, once the mounting brackets were installed, the hose fittings didn’t have clearance, and I had to fall back to a 16"x20" condenser for the Bav. However, a quick set of measurements in the nose of the E9 showed that that 16"x22" unit probably was the right size for E9, so rather than returning the condenser, I held onto it. For three years.

Early this summer, I finally rolled up my sleeves and had at it. Out came the E9’s radiator and its serpentine flow condenser. I test-fit the 16"x22" parallel flow condenser with a pair of “short-drop” hose fittings on it into the nose, and verified that it was indeed the right size. As a rule of thumb, the actual width from the left-most edge of the condenser’s mounting rail to the right-most edge of the short-drop fitting adds about 3" to the quoted width of the condenser. The 22" condenser, with 3" added for the brackets and fittings, comes to 25". In the E9, there is about 27 inches of space side-to-side in the nose. That leaves 2" for mounting brackets and getting the hoses on. You can try getting another inch out of it, but leaving 2" of space is a safe plan.

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I could’ve moved up in size from the 14" Spal fan I’d installed 18 years ago to a 16" fan, but to save money, I reused the fan, zip-mounting it to the new condenser. I have mixed feelings about this, and have mounted fans different ways on different cars, but these low-profile Spal fans are fairly light, and I haven’t had any problems using this simple mounting scheme.

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thehackmechanic

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I went to great pains to mount the new condenser in the E9 by re-using the mounting holes I’d drilled 18 years ago. (Nowadays I’d never drill holes in the body panels of a 2002 or an E9, but, hey, they were already there.) Once I began to carefully line things up, though, my initial reaction that “it fits fine” was tempered somewhat. I’d originally shock-mounted the previous condenser using the same rubber mounts with threaded studs used on tii fuel pumps, but for a number of reasons, the new condenser needed to be stood further out from the nose panel, requiring me to use fixed metal spacers for stand-offs. I also needed to cut a few inches off the bottom right corner of the condenser’s mounting bracket to clear a piece of sheet metal in the lower corner of the nose.

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I assumed I'd simply re-use the old mounting brackets, but one of the maddening things about these universal condensers is that their hole spacing is not standard; some have a ½" hole spacing, some use 9/16". In this case, the old brackets had a different hole spacing than the new condenser. The result is neither pretty nor elegant, but no E9 was further harmed by drilling during the installation of this condenser.

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With the condenser mounted, the next task was adapting the hoses. I was thrilled to find that I was able to cut off both the lower and upper hose fittings from the condenser hoses and crimp new ones on in place.

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Then it came time to address the question of converting the system to Freon. There are many issues here, and I’ll leave most of them for my next book (I was quite serious about the book), but, long story short, when converting between R12 and R134a, you need to remove all traces of the old refrigerant and lubricant, and that means flushing the system, and that means having to remove the evaporator assembly from up under the dash and disassemble it so you can flush the evaporator. Removing and installing the evaporator assembly in the E9 is one of my least-favorite automotive repair jobs. It’s nerve-wracking. The ductwork is 43 year old plastic, and it cracks and then shatters if you look at it the wrong way. The vinyl on the sides of the console tears easily. And the side pieces of the console are made from ancient particle board that spontaneously dissolves like doppelgangers of lovers in 1970 horror films. No, on more careful reflection, I was not going to pull that evaporator out unless I had reason to, like it was leaking. The R134a had a reprieve. For now.

I replaced the receiver-drier, pressurized the system with nitrogen to leak-test it overnight, and in the morning found that the pressure was down. Using Big Blu soap solution, I discovered a leak in the hose fitting on the other end of the lower condenser hose—the end that still had the original fitting. The hose didn't have sufficient length for me to cut that fitting and re-crimp it, so I made another hose and installed it.

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I then pressure-tested the system overnight again. When I was convinced it was leak-free, I evacuated it and recharged it with R134a.

So, although cost-wise it was easy (the parallel-flow condenser cost only about fifty bucks), needless to say this was not a plug-and-play operation.

And… the results are okay, but not transcendent. Once I’m under full sail, I’m seeing 43 degree vent temperatures. The system seems to run a little colder than it did before, and perhaps cools down a little quicker, but it still doesn’t come close to the instant-on-freeze-your-knee-caps quality that the Freon-equipped tii and Bavaria have. Of course, that could be due to some other issue. The system might not be properly charged. The expansion valve might be sticky. And there’s no question that the blower fan in the evaporator assembly is a little anemic.

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But really, this is all the warm-up (the cool-down?) to the bigger show, which is a from-scratch retrofit of a/c into the Euro ’79 635CSi, a process that is already underway one piece at a time. I face the same R12/R134 issue. Some folks have been trying to bend my ear on R152a. I’ll begin writing about this soon. Hopefully the series will have fewer than 701 installments.

--Rob
 
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Stevehose

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no way to flush out the evap without removing? Like pump a bunch of r-12 oil through then blow it out, that might suffice for these old units. r-12 works better and is less likely to leak.
 

thehackmechanic

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Steve, although I believe that, at room temperature, the expansion valve is naturally in its open state, "open" is still a severe restriction as compared with the evaporator with the expansion valve removed. I've tried "flushing through" the expansion valve with the evap assembly in place, and the flush kicks back through the port where you're trying to squirt it in under pressure. You can try to "pop flush" it this way, but it's very messy.
 

Stevehose

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That sucks

Steve, although I believe that, at room temperature, the expansion valve is naturally in its open state, "open" is still a severe restriction as compared with the evaporator with the expansion valve removed. I've tried "flushing through" the expansion valve with the evap assembly in place, and the flush kicks back through the port where you're trying to squirt it in under pressure. You can try to "pop flush" it this way, but it's very messy.
 

Gary Knox

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Rob,

Did that exact upgrade on my '74 early rhis spring. Great writeup. And pix.

I aiso put in a new genuine Sanden compressor and drier along with new hoses, I had about 15 lbs of R-12, so used dsome of that.

With an ambient of 80 F, the engine warm, the hood up, and a rpm of 2K my center vent air temp at medium fan speed and coolest rheostat setting is 33 F.
 

sfdon

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For those who can't decide which gas to use, carquest sells oil that is compatible with both. Super premium ester. You can try both r12 and r134 without flushing.

Developed specifically to lubricate compressors using R-134a refrigerant. Includes additives to prevent acid formation and corrosion. Contains conditioners and inhibitors for superior lubricity and compressor protection. Compatible with R-134a and R-12 refrigerants.

CCM CQE127 CCM CQE31 CCM CQE7

CARQUEST® Ester Oil Without U/V Dye, Gallon CARQUEST® Ester Oil Without U/V Dye, Quart CARQUEST® Ester Oil Without U/V Dye, 8 oz.
 

Blinkling

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Hi Rob. I bend people's ears about R-152a. Inspired by yours and other AC write-ups a few years ago I put a system in my car (stock evaporator but modern everything else). When the shaft seal went out on my Sanden knock-off compressor I fixed it and recharged with Duster cans from Home Depot using a side-tap for the cans. That's R-152 for you: it's sold to the public with the explicit purpose of being discharged into the air so you can use it guilt-free if that aspect appeals to you. And it doesn't come with the COR charge that R-134a does in California now.

As for performance, I get air below 40 degrees on an 80 degree day with the fan on high, and I can go below freezing at almost any outside temperature with the fan on the almost-highest setting. It seems colder now with 152 than it did while it had 134 in it. So far so good!
 

thehackmechanic

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Don, yes, ester oil is compatible with both R12 and R134a. It's what I filled the system with 19 years ago, and it's what I re-filled the compressor with when I pulled it out, drained it, and re-filled it as part of the parallel flow condenser installation, though I didn't write about it. So, yes, I can go to R12.

Blinkling, I've heard tantalizing things about R152a from a number of sources. I have no first-hand information. I'm embarking on a from-scratch retrofit into my '79 Euro 635CSi, so I may give it a good look.
 

sfdon

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Starting in the e23 series the expansion valve was actually outside the evaporator box.
Every shop had a drilled out valve to attach and then flush.
Not so on our little e9
 

bluecoupe30!

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This exchange is very useful, but I wonder at all the variables at play here. On the one hand we have Rob trying to get some cold a/c into his E9 in one of the hottest regions in the US when you add the humidity. Then there are others who live in the West who just have heat, and have their own experiences with their original or "upgraded" a/c systems. Some are happy, some not so much. Plus, there is the question of the expansion valve "fitness" as pointed out by Rob in his comprehensive description of his devotion to get cold air inside a Coupe. Blower efficiency, size of condenser, fan selection, choice of refrigerant, even vent size and quantity of vents are variables. I have parts for my a/c install on the shelf (yes even console faceplate, evaporator+++) but am waiting to fully understand the additional upgrades that would make this install worth the intervention) I really would prefer to have everything new and optimized from the start, and judge results from there. I have done the heater bypass, and this has made a world of difference, but on a 30 degree C day, I really need a/c! Keep the comments coming! Mike
 

sfdon

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Rob- we need you to figure out how to add an extra vent for the AC....
My elbow is frozen!
 

rsporsche

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i've been thinking about putting the bavaria duct into the coupe with the two side ducts ... and find a way to distribute air to the sides of the car
 

Luis A.

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Nice write up, as usual, Rob.

The Bavaria side outlets are not as much of an improvement as you may think. I had 40 degree air blowing through the center vents of the E3 but by the time it made the trip to the side vents it was lackluster. The blower just doesn't have enough CFM to push enough air, cold or not, to the side ducts.

Another variable that I have started to control for as I do AC work on vintage cars is the oil in the vacuum pump. Dump it after after one or two vacuum sessions, and if it has been sitting in the pump for a few months. And buy quality oil. I don't have a micron gauge so I've just let the pump run for a few hours (4-6) but I'm confident if I had a micron gauge I could see the difference between the fresh oil and not. Also, if you are doing this in winter in a cold garage (40-50 degrees) it takes a deeper vacuum to be able to boil the moisture and suck it out of the system and into the pump. At 80-85 degrees it only takes a moderately deep (28.7-28.9 " of Hg) vacuum. So get it done now before winter sets in!
 

rsporsche

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take a look at the picture - see the duct (part 13) ... this is what it looks like on a bavaria and the bavaria has a round vent next to both doors. even though the coupe uses this same drawing, we know that the duct does not have the side ports. there is no room to do anything between this duct and the vent grilles. the problem is trying to find a place to put the new vents on either side. perhaps on the drivers side there is a way to do it on the panel under the steering column.

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bluecoupe30!

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I have thought about the extra vent as well. See photos. Two are of an evaporator, next is an intermediate piece from an a/c equipped E3 on top, and another from a non-a/c Coupe. Some owners have adapted the non ac intermediate piece to fit buy cutting the bottom out to match the opening at the top of the evaporator unit. The E3 intermediate piece has those ducts that feed air to the vent openings at the ends of the E3 dash. I would like to add a vent in that steering column, under dash pad as Scott suggests and this E3 intermediate piece would only be about 6 inches away, as opposed to the 20 inches or so as shown, in an E3 dash. Getting closer. Now Luis points out the correct oil in the vacuum pump is important too. Plus I would like to find a way to get more out of the blower motor. Fun times! Mike
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