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I found one (originally made for a 2007 Land Cruiser).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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Blinkling

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I can confirm the success of the can side-tap way! And I managed to get an open box of six unused cans of R-152 from eBay for around that price. I was going to say that the things are probably $9 apiece from Home Depot now (inflation for sure). But that's still cheaper than R-134a by a little bit.

The can should say "difluoroethane" on it.

^^ I also have a relay that controls my fan via temperature probe. I LIKE it. I have the sensor strapped to my receiver/dryer and I have it set to come on at around 110ºF (30ºC). It's a cheap eBay import module. We'll see if it lasts. I made a little plastic case for it. In case it dies I still have my trinary switch which will engage the fan based on pressure -- they're wired in parallel so they're redundant.
 

ATL_Alan

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Prior to installing the Ireland engineering AL radiator, I did install a manual override switch that would turn on the AC condenser fan whether the AC was on or not. Was just a simple relay added and a switch under the dash. Used it occasionally when temps creeped up, but don't remember using it after the AL radiator.

Thanks
jjs2800cs
Hi, can you describe the relay you used for this? And does it connect to the same line that powers the compressor and condenser fan?

Thanks, Alan
 

jjs2800cs

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Hi, can you describe the relay you used for this? And does it connect to the same line that powers the compressor and condenser fan?

Thanks, Alan
Sorry for the late reply

I used something like this, typical relays found all over ebay and amazon


Basically spliced in the relay to the fan. When relay is off, fan will operate normally being turned on/off by the system. When relay is switched on via a switch under the dash, 12 volt is applied to the fan whether AC system is sending 12V or not.

Hope this helps

jjs2800cs
 

Dick Steinkamp

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Alan,

Just to expand a little on jjs2800cs's description...

There are two basic ways to wire your AC system. Using essentially all stock wire routing and electrical devices, or adding a trinary switch and related wiring and electrical devices like a more modern system. Both are pictured in post #44 of this thread and described.

With the stock system, you will need to add a relay in the heavy wire between 7 and 9 to connect it with the heavy wire between 9 and 13. The relay would close and send power to the condenser fan when activated. It would be activated with the switch under the dash that would send 12v through a light wire to the relay. The 12v to and from the under dash switch could be either switched (only works when the ignition is on) or not switched (direct from an always hot 12v source)

If you are running a trinary switch, you only need the under dash switch to provide an additional ground on the blue wire running between the trinary switch and the relay controlling the condenser fan.

Blinkling adds an optional circuit in post #46.
 

jjs2800cs

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AC update, Finally we are getting to the finish line in our restoration including the AC upgrade with Blinkling's replacement evaporator.

Yesterday we evacuated and charged the system now using R134a. So new Sanden (real one), new parallel flow condenser,, all new hoses made in house, and of course the replacement evaporator.

We do have a small leak which we will address at the connection between the larger copper line going through the firewall and coming from the compressor.

This is a flare fitting and hope a slight loosen and retighten will fix.

Got the system blowing cold with 2 -12 oz cans of 134a, was a struggle to get the system to empty the cans but we got there. Not sure why.

Since we still do not have front or back windshields in, cant really make a determination as to vent temperatures as of yet. Hope in the new few months we can give a definitive assessment of the new evaporator performance as it heats up here in Florida.

Cudos to Blinkling for taking the time to develop and offering the parts. Here are a few pics of my fitting the unit.

Thanks
jjs2800cs

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Blinkling

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I'm so happy to see another one making cold air! More cold air than mine, in fact, on account of me using the fake Sanden 508.
 

jjs2800cs

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Another update on AC with Blinkling's evaporator

Finally go the car together after 3 years, 4 months, and 4 days! So last thing (yea the last thing - right) to do is get AC working as starting to heat up here in Sarasota.

As reported a few month ago we are still chasing a small leak.

We added some refrigerant and dye, and finally got 30psi low and 175psi high pressures, which are in the ballpark for the conditions.

Yes we leak tested with the soap bubble stuff-nothing found. Also see no dye anywhere, and we also have a sniffer, and no detection anywhere as well.

So we will check the system after using the car and running the AC in a few days.

While charging the system, the compressor kept shutting off, even with the temperature knob turned to max. Could not get vent temperature below 50 degrees.

When I installed Blinkling's evaporator I just shoved the capillary tube behind the evaporator and near the expansion valve in that area. My thinking is I will probably always want the AC running at max or near max here in FL.

50 degrees is not going to work here in FL. So we bypassed the temperate knob and set up our own on off switch for the compressor and aux fan. Once done we got down to the low 40 degrees.

So not sure what is going on with the high temperature cutout. Is the switch bad? It does work as by turning it counterclockwise it does cycle even at higher vent temperatures. The other thing, is the probe must be seeing really cold air where it is placed? If it was in a warmer area it would not shut off until it got to temperature. Does this make any sense?

I have learned that some of the temperature switches have an apparent range adjustment on the back. I am fairly sure my does not.

So Blinkling's upgrade does seem to be bearing fruit, if I can get this temperature issues solved.

Any ideas on what to do other than pull out the face plate and examine or change the switch. I did check it before installing in ice water.

As for the leak, we will keep looking.

Thanks

jjs2800cs
 

Blinkling

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Thanks for the update! Here are some puzzle pieces that might fit your puzzle:

-Nice work using the ice water. There are also some newfangled electronic thermostats using thermistors which would probably be a significant upgrade over the old mechanical type. You'd likely want to connect the thing to engage a large automotive-sized relay for actual compressor control. I'm using one similar to this to run my condenser fan: https://www.ebay.com/itm/295549367961

-You can adjust your temperatures by taking some refrigerant out; If you are seeing a condenser temperature that is a few degrees too high and an evaporator temperature that is also a few degrees too high you can lower both this way. Wait for the whole system and the engine bay to be fully hot and then measure the temperatures and/or pressures.

-The more directly in contact with cold metal the temperature probe/switch is the more rapidly it turns on and shuts off. If you put it roughly in the back of the box where it will be measuring the chilled air it should work fine. It is, however, likely to switch off at a lower low temperature and switch the system back on at a higher high temperature (for instance 27º-off and 60º-on vs. 35º-off and 52º-on). No matter the location it should continuously call for cooling on a hot day. Post #36 above may be of interest.

-I'm sorry to hear about your leak. Based on what you describe I wonder if it's the compressor shaft seal. This would present as a leak most likely when the system is running making detection by sniffer or flashlight pretty difficult. It might not leak at all when off. Is it a new compressor?
 

jjs2800cs

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Thanks for the update! Here are some puzzle pieces that might fit your puzzle:

-Nice work using the ice water. There are also some newfangled electronic thermostats using thermistors which would probably be a significant upgrade over the old mechanical type. You'd likely want to connect the thing to engage a large automotive-sized relay for actual compressor control. I'm using one similar to this to run my condenser fan: https://www.ebay.com/itm/295549367961

-You can adjust your temperatures by taking some refrigerant out; If you are seeing a condenser temperature that is a few degrees too high and an evaporator temperature that is also a few degrees too high you can lower both this way. Wait for the whole system and the engine bay to be fully hot and then measure the temperatures and/or pressures.

-The more directly in contact with cold metal the temperature probe/switch is the more rapidly it turns on and shuts off. If you put it roughly in the back of the box where it will be measuring the chilled air it should work fine. It is, however, likely to switch off at a lower low temperature and switch the system back on at a higher high temperature (for instance 27º-off and 60º-on vs. 35º-off and 52º-on). No matter the location it should continuously call for cooling on a hot day. Post #36 above may be of interest.

-I'm sorry to hear about your leak. Based on what you describe I wonder if it's the compressor shaft seal. This would present as a leak most likely when the system is running making detection by sniffer or flashlight pretty difficult. It might not leak at all when off. Is it a new compressor?
Blinkling

Thanks for the reply

Compressor is new and is a real Sanden, think 508.

I have removed the existing thermostat/capillary tube. What a job removing the faceplate and shift console, radio etc. Pulled the capillary tube out of the opening. Not sure how I am ever going to get it back in without taking the who unit out, I will not do that unless absolutely necessary ouch!

Anyhow, I am going to try to reinstall an aftermarket thermostat/capillary tube as I have done some testing with ice water at 32 and 45 degrees with 3 different thermostats.
The one removed, a spare, and the aftermarket. The one that was removed when put warm into 32 degree ice water, it immediately opens with the knob at max. The other 2 do not. I have to slightly turn the adjustment just a few degrees counter clockwise before the switch opens. Interesting! I see no range adjustment on any of the 3.

So we will see in a few days if this makes any difference.

As for the leak, interesting about the shaft leak. Might it seal with use as the new unit sat for a couple of years before getting installed?

I have used similar electronic temperature controllers like the one you show the link to. I use them to control the temperatures in the various zinc plating bath solutions. I use them to switch a relay on/off suppling the bath immersion heaters voltage.

I like the idea of maybe using one of these as you suggest instead of the capillary tune setup. Maybe take off the glove box and shove the probe end in past the opening where the copper pipes come out???

Thanks
jjs2800cs
 
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jjs2800cs

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Another update!

Based on my ice experiment with the 3 thermostats I decided to install the after market unit as it has the longest capillary tube for the following reason.

With the AC console in place the access hole to slide the capillary tube back into the unit is not directly accessible as the exit duct sits directly above the hole. Look at my photos above with Blinkling"s evaporator. So we did the following.

Using the longer capillary tube we snaked it inside the right side console cover above the fan and pushed the end of the tube in through the opening where the two copper tubes exit the housing. I got it positioned so it does not appear to be touching either of the tubes. The tube was pushed at least 6 inches or more. So I hope it is hanging in the cavity behind the exit of the air thru the evaporator.

Started car and once warm, turned on AC with thermostat and fan on max. In very little time we saw vent temperature of 35 degrees. The outside temp was 75 with 60% humidity. All the car windows were down as power window switches are disconnected since the shift console is removed. So we were not going to cool down the interior.

After a few minutes I turned the temperature knob a few degrees counterclockwise and the compressor shut off. Then turned it back to max and it kicked back on at 41 degrees.

So it seems we might have had a badly adjusted range on the original thermostat. It is suppose to be hotter here tomorrow and will road test once get everything back together.

I do have some doubts about my placement of the sensor tube, but if it works, it beats taking the entire console out. We all know how much fun that is.

Here are a couple of pics of the capillary placement.


Thanks
jjsandsms

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