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Subject: Air conditioning compressor replacement procedure (long, with plenty of pics) Author: davidc (moderator) : member since December, 2003 : 10060 posts Posted on: 2006-08-29 09:18:49

For some reason, even though my father's 1998 BMW 750iL only has about 68,000 miles on it, the air conditioning compressor stopped compressing. Over a period of a few days, the car gradually started blowing warm air. After checking to see that the compressor was indeed engaging (to rule out electrical problems), a pressure test showed that the low side and high side were nearly the same, indicating that the compressor itself was at fault.

This article shows how to replace the air conditioning compressor and the drier/filter. Special thanks go to Joe Couture (JoeC) for lending his expertise and his time to show my wife and I how to tackle this job on our own. FYI, my local BMW dealer quoted $1,100 in labor alone to fix the air conditioning. We did it ourselves for $475 for the compressor, $45 for the drier/filter and about $20 in R134a refrigerant and oil. Total time was approximately 4 hours.

You'll need the following tools and supplies:
universal joint
10-inch socket extension bar
10mm and 13mm sockets
6mm allen wrench socket
philips screwdriver
vacuum pump and gauges
scale

You'll also need the new compressor, drier/filter, 1.5 pounds of R134a refrigerant and approximately 8 ounces R134a-compatible ester oil.

BTW, if any of you find yourselves in the Dayton, OH area and don't bother to make Joe's acquaintance, you're missing out on a true BimmerBoard comraderie experience. His enthusiasm and willingness to help is truly unique.



The new (remanufactured) Denso air conditioning compressor. $475 at BMA Auto Parts after a $75 core charge.

First, have the refrigerant evacuated from the system at a shop. My system had a leak, so I didn't have to do that.


You don't have to have a lift to perform this job. Just drive the front end up on some solid ramps. Be sure to engage the parking brake for safety.


Start by removing the passenger-side air filter box. This will allow us easy access to the compressor and drier/filter ($45 at BMA).


With the airbox out of the way, you can see the metal pipes going into and out of the drier/filter cannister.



Under the engine, loosen the belt tensioner so that you can slide the belt off the compressor pulley.





Remove the black electrical connector plug at the top of the compressor. Then remove the two allen bolts that secure the metal fittings for the rubber hoses going into and out of the compressor. It helps to have a universal joint and an extension. The second allen bolt is not visible in the photo above -- it's located to the left (rear) of the compressor). Take care not to damage the O-rings on the metal fittings as the new compressor doesn't include them.


Remove the three long bolts (two in the rear, one in the front) that secure the compressor to the engine.


This photo (of the new compressor) clearly shows where the two allen bolts are located, along with the three longer bolts and the single electrical plug connection.

Now you can remove the old compressor from beneath the engine.


The new (top) and old (bottom) compressors, side by side. You'll remove the blue and white plastic caps on the new compressor before installing it (take care not to let any debris enter the holes).

Mount the new compressor into the space where the old compressor sat, then install the three long mounting bolts. After that, remove the white and blue plastic caps and connect the rubber hoses to the compressor, tightening the two allen bolts. Don't forget to reconnect the black electrical plug.


The new compressor installed.


Now it's time to work on the drier/filter part of the system. Disconnect the electrical plug from the green connector.



Now remove the two allen bolts to free the metal pipes.



Remove the three screws that attach the black mounting plate to the body of the car and lift out the cannister assembly.


Note the location of the cannister and holes relative to the mounting bracket. The new drier/filter is on the right, ready to be installed. Also, note that the two rubber plugs are still in the new drier cannister. Because we don't want moisture in the ambient air to contaminate the dessicant within the cannister, the plugs will remain in place until the very last minute when we reconnect the metal pipes.



Unscrew the mounting bracket to insert the new drier/filter cannister.


Re-install the mounting bracket with the new drier/filter into the car. Tighten the three screws before connecting the metal pipes as one of the screws is difficult to reach with the pipes in the way. After that, remove the two rubber plugs, connect the metal pipes and tighten their allen screws. Take care not to damage the O-rings.

Now that you've got everything installed, it's time to pressure-test the system for leaks.



Joe added pressurized nitrogen to the system (through the low-side port).



Once the system was pressurized, we sprayed Big Blu micro leak detector (you could use soapy water, too) on the fittings at the compressor and the drier/filter. If no bubbles form, you're ok. Otherwise, there's a leak in which case you might tighten the connections or check for damaged O-rings. We didn't have any leaks so we proceeded to evacuate the system to ensure that no moisture was in the system.


Big Blu micro leak detector solution. This is what we sprayed on the fittings at the compressor and the drier/filter to check for bubbles, which would be signs of leaks.


Joe attached a vacuum pump to the system, along with the micron vacuum gauge. The goal is to eliminate any moisture in the system. This process took about 45 minutes.

While you're waiting, use the time to re-attach the belt around the compressor pulley and tighten the tensioner below the engine.

If you don't have access to a vacuum pump or gauges, nearly any air-conditioning repair shop should be able to evacuate and charge your system for a nominal expense (under $50 by my estimate).


Joe's micron vacuum gauge. Regular dial gauges don't tell you everything you need to know. This baby lets you know that you've got all the air/moisture out of the system before we start charging it with R134a.


After fully evacuating the system and ensuring that no moisture is present, the next step is to reassemble the air filter box, then charge the system with R134a refrigerant. To do that, Joe attached a cannister of R134a to the low side port of the car, with the engine running and the A/C and blowers on maximum. Before starting, the scale was zeroed out so that we could accurately measure 1.5 pounds displaced from the cannister into the system. After that, I added 8 ounces of R134a-compatible ester oil (Interdymanics can, $6 at AutoZone) to ensure that the the compressor has sufficient lubrication.


Proof that the new compressor is functioning as it should, producing a cool 49 degrees at the vents.

David Cecil

'97 740iL, 145k miles
'92 750iL, 88k miles
'86 735i, 101k miles

Visit e38.org for everything technical about your BMW

• Air conditioning compressor replacement procedure (long, with plenty of pics) (pic) (url) - davidc 2006-08-29 09:18:49 (6899 views)
  • Another wonderful post David. Many Thanks. (nt) - farnarkler 2006-08-30 08:22:42 (121 views)
  • What was the temperature and humidity, engine rpm when - kw740il 2006-08-30 04:12:28 (142 views)
    • Outside temp was ~ 95 degrees, high humidity, 2000 RPM (nt) - davidc 2006-08-30 05:35:42 (136 views)
  • Autozone has Lender guages and vacume pumps free. (nt) - kw740il 2006-08-30 04:04:07 (190 views)
  • Is that a block heater I see in the fifth large pic, in front of the oil pan? (nt) - kc314 2006-08-29 21:12:13 (157 views)
    • I was wondering the same thing. If it is, the previous owner (pic) - davidc 2006-08-30 01:26:48 (294 views)
  • dave, you really did use those pic's--good job! (nt) - JoeC 90 750il 89 735il 98 740il 2006-08-29 11:30:30 (106 views)
  • If I was a moderator, LOL, I would immediately put this on e38.org. - collison944 2006-08-29 10:44:09 (103 views)
    • JoeC already had the vacuum pump. I'd like to find one to buy. (nt) - davidc 2006-08-30 00:15:34 (115 views)
      • HarborFreight has them as of 4 mos ago. (nt) - bmw635 2006-08-30 00:45:30 (129 views)
  • Nice post. Turkey thermometer is the best lookin/feelin' pic (nt) - collison944 2006-08-29 10:41:18 (107 views)
  • Great post! Highly detailed.....almost ''Magnum-esque''. Kudos to JoeC. (nt) - Peter 2006-08-29 10:02:12 (92 views)
  • Oh now this one I like, gotta' get back to reading it. THANK YOU....! (nt) - Magnum 2006-08-29 09:21:41 (116 views)
    • Is your A/C malfunctioning? (nt) - davidc 2006-08-29 09:32:34 (275 views)
      • No, but it will some day and now I will diy it. (nt) - Magnum 2006-08-29 09:37:25 (135 views)