DIY - Aftermarket Evaporator Installed In A Coupe

Hi Team. I set out this year to find a replacement evaporator for the AC systems in our E9s and E3s (and E12s and E21s).

I found one (originally made for a 2007 Land Cruiser). It fits in the original box pretty well and it’s in my car working now. I’ll show you how I did it and then update you at some point in the near future as to whether there’s any advantage to it over the original parts. This is a work in progress and you are joining me in the experiment!

I want to emphasize that many members on this board have made their AC systems work pretty well using the original BMW parts and that if you are in need of better cooling in your car start with the basics by making sure your system is charged with the correct amount of oil and refrigerant; making sure that you’ve cleaned the bees out of your condenser; inspecting your switches and wires; checking if the seals are still there on the little flappy doors inside your heater box; and seeing to other correctable things.

On the outset, I wanted to find an evaporator upgrade method made from cheap, commercially available, and reliable parts that could be shared as a DIY guide that anyone could follow. How’d this turn out?

Is it an upgrade?: TBD
Is it cheap?: Pretty affordable I guess. See the spreadsheet below.
Is it reliable?: I already feel better knowing that the connections have o-rings, not copper washers.
Are the parts commercially available: Most yes, some no.
Can anyone do this?: Yes, except for a few parts which are hard to fabricate. Read on.

Here is the stock evaporator box with its big tube-and-fin evaporator.

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Here’s the old evaporator and associated plumbing.

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Here are the new evaporator, thermal expansion valve (“TXV”), and associated plumbing:

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I modeled all of these parts to make selecting an evaporator from the Internet easier. You can see here that this new evaporator isn’t quite as tall as the old one but it fits in the box snugly against the blower cavity despite not being quite as tall as the old one.

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Below are all the parts needed for this conversion as well as a source for them (in the spreadsheet). This assumes you have an original AC box with a working blower assembly and that you’re willing to modify the box.

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Here is the kit assembled and in the box (top view):

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Thoughts and reflections:

I’m pleased! It’s been cloudy but I got a sunny day today finally. I got a chance to run the system starting with an interior temperature of 107º. I was measuring temperature drops (measurement of air going in minus air coming back out) of as much as 35º as the cabin cooled down. I’m going to keep tweaking some things to see if I can get more cooling.

I didn’t make any modifications to the blower even though it is probably the biggest limitation in this system. I’ve determined that the blower (with whichever evaporator is in the box) makes about 190 cubic feet per minute of airflow. If I’d found a way to switch the blower and the evaporator at the same time in this experiment there’d be know way to know which made the bigger difference.

I wanted this to be made completely from parts anyone could source. The 3D printed stuff I’m kind of excusing here since there are probably dozens of ways to secure an evaporator in a plastic box and 3D printing was just the easy way for me. Also, I can share those files with anyone who wants them.

As far as the fit of the new system, it was kind of a bummer that the TXV interfered with the back of the box since it was almost a perfect match. Have a look at this cross section:

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View from the bottom of the valve and the box cutout:

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A window shaped like this needs to be cut out from the box. Aside from that, the only other modifications to the box is a few screw holes.

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The blue plate (part D4 on the illustration) is a shell that makes a little more clearance around the TXV (particularly at the bottom) and also collects dripping condensate and returns it to the bottom of the box using gravity. I have it installed pressed against a foam seal and I’ll be checking it periodically this summer to make sure it doesn’t leak. It could also be glued in with silicone.

The real missing link I couldn’t find on any website was an adaptor from that particular TXV to an O-ring-stye connector and a clamp to squeeze them on. I’m referring to parts C3, C4, and F on the diagram. I made the adaptors on my little lathe and brazed them to tubing.

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This was my first time brazing. It seems to have worked well but I know this option isn’t easily available to everyone at home.

Presumably I or someone more experienced than me could make this assembly into a kit if the DIY route is too confusing. Also, I took all the pictures needed for a full "how-to" guide. But I think anyone with enough ability to take their box out of their car and / or charge up an A/C system should be able to assemble this.

I have enough parts for another prototype if someone with time on their hands wants to reimburse me for just the parts and postage. All I’d ask is that you’d be able to compare this system with the previous one in your car and report back for everyone’s benefit.

Anyway, it can now be said that someone has used a non-original evaporator in an E9. I’ll post a critique of the function soon. So far so good. Thanks for following along!
 
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Ohmess

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I've not had my dash apart, so I am probably not the best person to address this, but I will toss out a couple of comments here, hopefully to get the ball rolling.

I think the heater box is self contained, with a fan to blow air over the heater core and to either the floor or the defroster (or partially onto both).

The a/c box is a separate box, which taps into the "vent" system. The "vent" system was originally designed merely to allow outside air in through the two vents in the middle of the dash. This could be operated in conjunction with the heater, to pass cold air over the driver's face and keep him alert for example, or separately.

I suspect BMW tapped into the vent system in order to make sure the colder air flowing over the a/c evaporator did not have to pass over heater core before entering the cabin. And I suspect "packaging" all of this within the available space was another reason for this setup.

So, my thought is that some modification would be required to join the heater and a/c box. This might be something that was left in place all the time (in which case some of the output from the heater would flow through the center vents), or rigged up with some mechanism to close off the connection.

All of that said, a more powerful blower likely would make a big difference, even if directed through the existing vents.
 

Blinkling

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With vent closed you in essence have recir, with it open you get outside air which will be warmer theoretically than air in cabin.

I think it’s the “Air” lever (on the left) that has to do with outside air. That’s the one with the rheostat. The “Vent” lever (on the right) controls whether air can move from the heater box to the dash duct, right? Both boxes dump into that duct.
 

HB Chris

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You are correct, when fully to the left all outside air is stopped according to the manual. But, the lower right is called a cold air lever and shuts off cold air completely. Opening it sends air to the center grille. In essence heated air can go to feet or defrost while cold air is coming from the center vent. Confusing to say the least.
 

ATL_Alan

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Wanted to let everyone know I'm the proud recipient of Blinkling's #2 evaporator (so memorialized by him on the case) and it works fantastically well! I'd been working on various engine cooling and AC issues this summer and had replaced a lot of components (all the big AC equipment except the original evaporator and valve), radiator, fan clutch, numerous hoses, thermostat housing and thermostat, water pump, condenser fan and the condenser fan thermostat switch. I also fabricated an aluminum shroud between the condenser and the radiator to focus the condenser fan and installed an electric heater bypass valve behind my 3.5 L motor with dual Webers. Thanks to all on the E9 forum who helped me navigate this (specifically Blinkling, Stevehose, sfdon, teahead, Ohmess, pickman, HB Chris, Layne, etc.) and patiently answered my idiotic questions. I started out as a complete newbie with some time on his hands and a desire for a working AC system.

With all new AC equipment and the original evaporator and expansion valve (which had been cleaned and tested), my high pressure readings were all over the map and the temperature never got below 50. The last time I tested it the vent temps went to 50 and then back up to 60. High side pressure was headed to 400 psi. Ugh.

I reluctantly (and I mean reluctantly because it's a PITA) disassembled the middle console again, extracted the original evaporator and contacted Blinkling. He sent his new evaporator and expansion valve assembly a few weeks later. I installed it over the weekend and charged the system. Now, as soon as I turn on the AC, the temp quickly drops, and drops, and drops. I stopped a few tests at 30 degrees (I let it go down to 29 degrees on one test just out of curiosity) before easing the vent temp back up. We'll see what happens when the temp and humidity are high again but at least now I know the system will definitely cool. With the Sanden, you hardly know the compressor is running and the engine temp stays steady.

If anyone has questions on any of this, let me know. But working with the E9 forum and Blinkling has been a privilege and a lot of fun and his evaporator assembly gets the job done!
 

Ohmess

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Hi ATL_Alan - Are these babies for sale? And if so, would you mind sharing with us how much they cost?
 

ATL_Alan

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You'll need to ask Blinkling; I had the new evaporator and valve already and just sent everything to him (neither is expensive). He did all the fabrication and sent me back the finished assembly. Since it was experimental, he billed me for his parts and shipping. Very professional looking and he's great to work with.
 

Blinkling

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Hi group. I owe everyone an update!

I’ve been running this kit in my car now all summer successfully. And I even made a friend trusting enough to beta test it too. Thanks to @ATL_Alan for the kind words and for going through the considerable effort to put the system in your car! I told him I hope he continues to chime in here with his experiences as he puts the system into regular, everyday use.

My observations from the summer are:

The most impressive cooling appears to happen at startup after the car has been sitting in the sun. With the air inside the cabin at ~100ºF I’ve seen vent supply temperatures of 60º and lower. Like Alan reports, if the ambient air temperature is in the seventies, the evaporator would be perfectly happy to drop below freezing (and ice over). A properly working dashboard thermostat should step in and prevent freezing. I also installed a low-pressure cutoff switch that intervenes when the suction temperature (back to the compressor) is in the low 40s.

Under regular operating conditions (with the car fully warmed up) it pretty much just spits out a constant stream of 52º air (according to the thermometer measuring the refrigerant going back to the compressor).

So all in all I consider it at least a minor upgrade over the old system from a cooling perspective and a significant upgrade in reliability. And the parts, especially the valve, should be available for a long time I would think.

So about making this a kit:…

I’ve had a few of you reach out to me about the availability of this, in a pre-assembled state, for your cars. I’ll continue to keep this thread updated as a DIY for machinists and experimenters but I will also be opening a “Shameless Commerce” thread now that I’m confident I can make these in batches. I just shipped one and I’ll be completing another one in a few days. I’ll add the link here as soon as I do that.

I made a couple of modifications to the 3D printed parts based on Alan’s experience — it turns out there is (normally) a brass tube that goes into the evaporator box before the capillary tube for the cold control / thermostat gets inserted. 3D printed part D2 therefore got an update and I’ll reupload those files (linked on the first page of this thread) soon too. You can insert the brass tube first if you have it, then the capillary probe. Or you can just shove the capillary probe in there.

An observation, though: as needed, and if you’re careful, you can probably drill a hole in a different part of the box and insert the probe. In my mind, there is still some debate as to whether this capillary tube is better off physically touching the evaporator like it did in the original design or whether being in the cold stream of air is good enough. I’m operating under the assumption that the latter is the case.

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This is a difficult place to have to install the capillary tube! The duct for the vent is usually covering the hole by the time it comes to put the probe in place. I made some of the part red to make finding the hole easier. If y'all at home print these parts out consider changing filament to a bright color at some point during the print or just slap some paint on there.

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Dick Steinkamp

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My Blinkling custom evaporator and TXV arrives this week :cool:. I have not considered getting the AC working in my E3 until Blinkling came up with this solution to the inefficient, outdated and prone to leak original evaporator/TXV. Even if I installed a modern compressor, condenser, receiver/drier, etc., I would still be stuck with the original evaporator/TXV and 6 ol' skool, tough to seal, original, flared fittings (all modern O ring fittings with Blinkling's set up)

I've got most of the other needed parts on hand and I have already instilled the new parallel flow condenser and other parts.

Thanks to David for inventing and producing this essential piece for us that want actual AC in our E9 or E3. and thanks to @ATL_Alan for being the beta tester...and to both for letting me pester them with lots of questions.
 

Blinkling

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And thanks for being such a willing "early adopter," Dick! It will be crucial to keep getting feedback from the several early kits and it has been a pleasure to talk about system planning with you.

@HB Chris and I are having a side-bar conversation about the temperature capillary probe and whether it needs to be in contact with the metal of the evaporator in order to function as originally intended. Recap: originally it was inserted inside that brass tube which was in turn jammed into the original evaporator fins. Obviously metal-to-metal contact results in faster heat transfer than air-to-metal but I wonder how much temperature difference there is, theoretically, between the metal of the upper evaporator fins and the air leaving the evaporator having been cooled. Could this affect the sensitivity of the "cold" dial on the dash board? I think @ATL_Alan drilled a hole in a different location on the box and inserted the probe there. Let's see if he is willing to confirm that.
 

ATL_Alan

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Initially, I drilled a hole in my plastic case and ran the probe into the fins of the evaporator because I couldn't figure out how the probe was supposed to go in Blinkling's setup. The new evaporator is shorter than the original so that hole needs to be lower to hit the fins. After he told me it just runs through the case in the original hole through his plastic piece (D2 originally - now updated) which forces it down onto the top of the evaporator, I did that and that's the setup I have now. There was no difference in ultimate temperature; I didn't clock the speed of temp drop between the two setups but in my final test, I was below 32 degrees in less than a minute (75 degrees outside), which was plenty fast and cold for me.

FYI, almost everything related to the AC system in my car is new except the original controls (condenser, compressor, lines, fittings, dryer, condenser fan).

I'll update this thread as we enter the steambath months here in Atlanta and let everyone know how it's going.
 

Blinkling

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Hi team.

I nominated a new location for the temperature probe. Here's what I'm thinking: through the middle, just right below the blower motor.

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Here's a view from the bottom of the virtual box:

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Not bragging but I managed to drill a hole in my A/C box without punching through and ruining the evaporator. The blue rod is my overly long 1/4" drill bit. You might want to drill this hole when you have your box apart. Actually, yes, be sure to do that.

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This photo might have much value but this is the hole once drilled:

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I tried inserting the capillary tube and it went just fine. The little fins on the evaporator are plenty flexible enough.

It couldn't hurt to put a little paint on the capillary tube at about the 4" mark so you know how much of it to push in. Four inches should be perfect.

This location has the added advantage that you can insert the tube long after you've put the vent and ducting back in. The original location is a drag.

You'll likely need to carefully coil your capillary use up some slack. This location is a bit closer to the actual knob than the original one.
 

HB Chris

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Just be sure it isn’t near the fan brushes, my coupe would blow the fuse for unknown reasons until I discovered the ether pipe would bounce and hit the motor.
 

ATL_Alan

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I located mine higher and to the right on the box to avoid everything before reverting to Blinkling's original setup. Either approach appears to work.
 

Blinkling

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Hi crew. A couple of updates:

Concerning the location of the temperature probe / capillary tube: I did a little experiment. With the dashboard faceplate in my car removed I tried the thermostat in two evaporator box locations while the car idled in my driveway.

The first location was the vent where the cold air enters the cabin. This is the same cavity you'd be "probing" if you inserted the tube in the original box location which (see Post #29 above) is now occupied by a 3D printed part.

The second location was the middle of the evaporator as detailed in Post #33 above.

Impression: Both locations work.

Environmental stats during test:
Outdoor temperature: In the sixties Fahrenheit.
Ambient temperature in the cabin: 73ºF
Sun load: winter, not cloudy.
Temperature of refrigerant going back to compressor ~46ºF
Engine speed: ~1500 RPM


The thermostat's job is to cut power to the A/C compressor clutch when the evaporator core gets to about freezing, wait for the temperature to warm up by a certain amount, and then switch the compressor back on to resume cooling. This prevents the evaporator from becoming an ice block. On a hot-hot-hot day the thermostat doesn't have much of a job to do; the system just runs at full power. On a mild day, though, the supply air temperature drops below freezing and the thermostat needs to intervene. I measured the supply air temperatures as it did so:

Vent location:

Kicks off at: 29ºF Powers back on at: 59ºF
Kicks off at: 30ºF Powers back on at: 61ºF
Kicks off at: 29ºF Powers back on at: 64ºF
Kicks off at: 33ºF Powers back on at: 65ºF

Evaporator location:

Kicks off at: 31ºF Powers back on at: 53ºF
Kicks off at: 34ºF Powers back on at: 54ºF
Kicks off at: 32ºF Powers back on at: 54ºF
Kicks off at: 33ºF Powers back on at: 55ºF

Feelings: The lower, middle-of-evaporator location is probably better.

As you can see, the second location, where the probe is shoved directly into the evaporator, allows to the thermostat to respond to the temperature changes a little bit quicker. I didn't time each of these cycles but the on/off/on/off etc. was probably about 20% faster with this method. On the other hand, if wear and tear on the compressor clutch due to cycling is a concern, maybe there's an advantage to the first location?

And again, this shouldn't make a difference on the days where the system is asked to do its maximum cooling anyway.

Oh, one caveat: I messed with the set screw on my thermostat so perhaps anyone trying this at home should experiment and see if their thermostat is in the same range as mine. Here I am dipping the probe in an ice/water mixture (which should provide a constant 32ºF value). I turned the screw until, on its lowest, most sensitive setting, the thermostat's switch would open when I put the probe in the ice and then close again when I took it out.

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Here's the set screw: It's visible when you pry the little door off the bottom.

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Blinkling

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Now I will share some knowledge passed along to me by @Dick Steinkamp. He is installing the new system in his car at this moment. This pertains to the "low-side" or suction tube leaving the evaporator kit and making its way behind the glove box to the firewall. (Actually: It pertains to both high and low pressure tubes but the smaller tube is pretty compliant and allows for more options.)

Up 'till now my philosophy with regard to the fittings poking out of the box has been "get them close to the locations of the fittings on the original evaporator and let the nice, compliant hose make the dimensions easy." This is silly: everyone is going to want to use the newer o-ring fittings. Accordingly, the location of the old copper hardware shouldn't factor in (unless the original flare fitting tubes are to be reused). It probably wouldn't be a big deal except for the tube needs to make a fast turn to avoid interfering with the glove box. Check it out: on my system I experimented by making an all-copper line with a bespoke male o-ring fitting which wasted precious minutes of my life I can never get back but fit pretty good:

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However: to my sensible compatriots who are using reduced-barrier sized #10 refrigerant hose (and the crimp fittings that go with it) this creates a perfectly annoying situation where the fitting is too close to the bend to use a straight fitting and too close to the box to use a 45º or 90º:

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photo credit: Dick

So, DIYers:

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Again, this advice will be most useful for everyone who wants to use rubber hose behind their glove box.

So what is the best way forward? Dick and Alan advise that if the fitting were to only just barely pop out of the side of the evaporator box that a straight hose fitting could be used and then the meaty, flexible part of the hose would be set up to start the curve where it needs to be.

To make this happen, the tube manifold should be made like so:

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This is how I will plan to make these in the future.

That said, the opposite can be done and the fitting can be made to stick out even farther so that a 90º fitting like this one could be used:

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I'll update once I've looked into this more. I'm ordering one now and I'll plug it into my model once it gets here.

So, in summary, and to clarify:

The low-side plumbing needs to come out of the evaporator box and then bend. There are many ways to make the tube but planning needs to be done with regard to the bend. The original bend happened at around 4 1/2" to around 5" (~117 - ~127mm) from the side of the box.

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ATL_Alan

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Thanks to Blinkling for the write-up on the tube locations; we've been having sidebar discussions on that for awhile. And many thanks to Dick for the capillary tube experiment! I put mine in where Blinkling's evaporator was originally designed to accept it but now I think I'll relocate it into the fins of the evaporator. While I have the thermostat out, I'll check the set screw adjustment as he described.

Great stuff, many thanks to both of them!
 
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