2006 X5 3.0 air conditioning diagnostics - looking for some guidance/roadmap
 

The AC stopped working on my wife's car last week. It's particularly poor timing as she's using it to make long trips at the moment to care for her father who has had a stroke & is in another state. Such is life. Our X5 has been a reasonably (actually well) cared-for vehicle and has given few real issues, but it does have 174K miles, so I expect things to break.

A cursory look at the AC seems to indicate the compressor is not engaging,
(belt turning, hardware on front of compressor is stationary) but connecting a gauge to the low pressure port shows high pressure (sorry, I didn't record nor do I remember what, but it did NOT read low). I think the aux fan is engaging as the routine test upon startup & it does engage when the connector at the high pressure switch is removed. I replaced the aux fan last year (symptoms were a few cooling system overheats and AC only worked when the vehicle was in motion) and I bought the hardware/software to set up a dedicated BMW scan laptop for her car at the time.

I don't have a full rig to vacuum the system & I'm not looking for a quick 'hack' to get it going, but as a lifelong DIYer, I would prefer to do as much of the initial diagnostics as possible & obviously (I suppose) if there is a simple fix that does not involve opening the refrigerant system, I'd most likely do that myself if I could ID the cause.

I have not checked fuses & have not checked any other electrical connections for fraying, wear,etc.

I'm assuming the next step is to see what the scan tells me. And, I'll assume that I'll be able to translate what it tells me into practical terms.

Is the compressor on this model one that can be simply/viably tested for + voltage w/ the AC on & even be jumped to test whether it's mechanically functional, or is it controlled via pulse signals like the aux fan?

Any other no-brainer checks someone may want to share from experience would be welcomed.

Any pointers to a system overview/exploded view/etc. online documentation of this AC system would be helpful of course also (I've only found various forum threads so far).

Thanks in advance.

subject vehicle: 2006 X5, 3.0 174k

It would probably be very helpful if you can repeat that test and take the readings, noting test conditions.

When the engine is off and cooled down, with enough time for the AC refrigerant to equalize throughout the system, you should get a reading around 50+ psi (guess), increasing with ambient temperature. So if you then start the engine with AC turned off, things in the engine bay will warm up, heating the "freon," and raising the temperature gradually with temperature increase, as some of it changes from liquid to gas. High-side pressure readings in this state should be the same as low-side.

So that testing ^^^ just checks if you've got freon in there, not necessarily if you have enough of it.

If you then want to test the AC, you need to set the system to run. The manual will have certain settings, but they are likely to be: minimum temperature setpoint (max cool), maximum fan, recirculate (basically settings to maximize the load on the AC system), and hold engine rpms at 2000 rpm. Ambient temp is also specified to be warm to hot.

Under those conditions, you should see a significant drop in low-side pressure as the compressor is sucking freon in. Down into the teens. It sounds like you may not have a high pressure gauge, but of course the high pressure should go up, well above 100 psi.

Hope the basic background info is helpful. That is all general AC information, and of course things would be better specified with the exact AC system you have.

But to keep it simple, since you've got the low-side gauge, take readings with the car off and stabilized, and then again with the AC running. Those simple readings will tell you a lot.

thanks. Oh, come to think of it, I do have one of the manifold rigs (HF cheapie...seems it needs some type of minor dial rehab but no big deal) that will read both sides. For simplicity, shortness of time...the X5 is in heavy use at the moment...I reached for the mechanic-in-a-can gauge rig on a can of r134a that has a gauge on it...low only...just read the gauge, didn't engage the can btw.

The BMW scanner gives me error 027 "magnetic clutch air conditioning compressor"

Sounds like a compressor, I'm assuming. Would anything else trigger this code?

If the car has low mileage such as 20K-30K, then I'd say replace only the clutch coil (aka magnetic clutch).

However, at 175K miles+, the AC compressor lives on borrowed time.

At this mileage ---> get a new compressor for the peace of mind and move on.

PS: Don't gamble with the old compressor, google "AC Black Death" and do some readings...

Yeah....assuming that's it, I'll likely hire it out to a friend who has a repair shop with all the proper vac/fill/etc equipment. I'd expect the compressor is not mentally or physically taxing but I'm not sure how much I "save" having to take it to his place before & after...or, hell, maybe it's worth it. Sad thing is we are about to sell it because we need a van for our growing family...

BEST thing you can do is to install the new AC compressor following the link I wrote for 1998 528i below:
DIY: 1998 BMW 528i 160K Replacing AC Compressor - Bimmerfest - BMW Forums

Then send the car to your friend for vacuum and recharge with R134a.

Indeed. Thanks. Will study this!

EDIT: read it...sounds straight forward. thanks again!

The air gap between the clutch and magnet might have changed so the magnet is no longer able to pull the pulley into the clutch.

SMA on youtube have several ac video ins which the fix was just a smaller shim.

so, I would be wise to check this gap? any reference to what it should be? I'll check that out also. Upon intense interrogation (kidding), my wife was not able to definitively report any unusual noises prior to the AC failing, so anything is possible. Sounds like a smart check though. thanks.