Hi rbjtech,
I just saw your Post and I thought I'd jump in with my similar experience with my 2004 X5 E53 4.4i AC system. I posted my questions about my problem on here, and on other assorted X5 E53 group forums. Advice varied from replace AC compressor, to replace Everything. Or let a shop do it. Here is a link to my Post from September 30, 2019.
https://xoutpost.com/bmw-sav-forums/...y-problem.html
I hope I pasted the link properly.
My AC mystery was Why did my AC system with No leaks and proper 134a charge cool like a meat locker all day at idle, but Stops all cooling once 2000RPM is exceeded. Pressures go from near perfect, to static-like Hi-Low sides near equal around 100PSI and no cooling. Dropping the RPM's after 2000RPM Never restores cooling or return of pressure differential.(Revving to 5000RPM as some suggested had no effect either.) AC Clutch Never disengages. Car off overnight and engine back to ambient temp, and AC will cool Great again..... But only up to 2000RPM.
This scenario just really bothered me. A mechanical system Broken cannot heal itself. So I started research into Calsonic-Kansei and their CSV717 "VARIABLE DISPLACEMENT" AC Compressor. Key Words there. It is Not displacement controlled externally via either electronic circuit, or even mechanically. So Where is it's Displacement controlled from?? A little part called the "MT2280 Pressure Control Valve". I was all set to buy a NEW AC compressor, evaporator, filter/dryer, etc. But......
I decided to take a chance on the cheapest version of that valve from my local Auto Zone. The "Santech MT2280" for $14.99 plus tax. Pics included.
Please be Sure to evacuate your r134a Before removing the circlip holding this valve into the bottom of the CSV717. I used Brake Cleaner spray to make things as dirt free as possible in case this actually worked. Ohhhhh, and did I mention yet that I Did NOT have to remove the AC compressor from the X5 to do this? I did it all in the driveway with the X5 up on 2 metal ramps giving access to the compressor. I used my crappiest old pairs of circlip pliers to bend them into 'contort' position to get the circlip off, then back on with the new one. ***Warning*** Even evacuated, your AC compressor is Still under held pressure internally inside the compressor! So when you pry and coax this little round nub out, get ready for a Pop of some 134 and compressor oil. (Always eye protection. And some rags handy.) I lubed the new valve's O-rings with new PAG oil to insert. About 6 attempts in, I got the new circlip retainer to stay in. Even with horrific heat that day (08/07/20) and not the best of working conditions, the whole MT2280 new replacement valve took me about 20 minutes. Then 20 minutes of steady vacuum pull to check for leak down. All Perfect. Then 90+ minutes of vacuum pump (because very hot and humid day. Extra Suck always Good. lol). Then proceed with no rush, mostly gas vapor r134a to 440 grams (0.97lbs).
By now, you know where my story is going. I bought this car in August of 2017 for $350. (The abusive owner used it as his contractor pickup truck. A whole other story. Didn't run, and pretty rough.) LOTS of sweat equity into this X5. But I Never could enjoy driving it in NJ because you Need Air Conditioning in your car here. And the AC evaporator is needed in rain and cold for interior window defogging.
So, the Results: My 209K Mile E53 X5, for the First Time since owning it (and probably years before me), has a Perfectly working AC System. At ALL engine RPM's. I went from hating this car and nicknaming it the "Xcrement5", to absolutely Love driving it now. It's a BMW, so of course, It leaks oil near everywhere. But now with the AC 'mystery' solved (by me... yeah. I'll take those props! lol), I'll get on the oil leaks. And doing the trans service fluid, filter, bridge seal, etc.
Here are a few pictures. I went with a subtle but clear lean to red from BMW blue on logos. And shades of metallic gray and varied textures. I know style is subjective. But I'm pretty happy. If any interest by this group, I'll do a story board post of my resurrecting this X5. I am Still well under $1000 for All I have done to date. And that $1k Includes my $350 purchase price
I hope this info can help you. I found nothing on the internet about this issue with the Calsonic's. But an Easy 2+2=4 for me after going to the Calsonic website and seeing How their AC compressors actually work. A small perk of the general 'Covid can't go out anywhere' time to use to explore on the Internet.
Best To You and Yours.
Stay Safe & Healthy.
And Hopefully Cool & Comfy now ;-)
Michael C. In Brick, NJ USA
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