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Discussion Starter · #1 ·
Hi

The air con on my E38 750iL does not work and one of my neighbours who does industrial air con servicing checked it out for me.

Pressure was spot on, but the air con will not switch on or the aux fan does not come on either, he jumped the compressor and the compressor kicked in and worked fine and the system was ice cold, condenser was fine too, no over pressure or anything.

He checked all the fuses and relays and they all seem fine as well, only problem we could see is the 4 buttons on the climate panel you struggle to see any of the buttons led's as they are very dim, though the screen/heated rear screen and recirc buttons do work, he wondered if it might be the control panel that was stopping the air con from working.

Any ideas what to check next as he phoned a mate who deals with car systems and he reckoned without starting to randomly replace sensors, i would have to put it into a dealer to get a diagnoses done.

Thanks
Colin
 

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Well mate, from my understanding your AC compressor is not engaging. Unless jumped. You've checked pressure in the system, relays, fuses and compressor still not engaging. I got that right?
1st Q :Does the led light in the control panel illuminates when you push the button? If not there is any way that you can check with a voltmeter if it's getting power?
2nd Q : You have said that you checked the pressure...It was reading 90-120 PSI on both lines? If yes you have enough pressure, if not you might need to add some freon.

What year is your E38 ? There is a TSB (technical service buletin) dated for 99 Sseptember and applicable for all E38, E39 and E46, saying that an issue for a ,,compressor not engaging " could be due to the pressure sensor at the high side line (at the dryer). Again with a voltmeter you can check for a resistance in there. At this time I don't know the specifications.

That was all that came in my mind for the moment.

Yes , if you take the car to the dealership you will save time in finding your problem, but I doubt you will save money too...

Good Luck!
 

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Discussion Starter · #3 ·
LED does light up, but the 4 buttons in a row are all dim when lt, though the functions work, i am wondering if the panel has been replaced and not coded to the car as i believe that if it is not coded, then everything works bar the air con.

Pressures were fine in both line and the car is an 07/1996

A guy that is local is breaking a '96 740i, so i am going to get the climate panel, get it coded and take it from there.
 

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LED does light up, but the 4 buttons in a row are all dim when lt, though the functions work
yeah...it could be bad or could have a poor ground connection.
Keep us posted anyway, I am curious what you are running into...
 

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when I lost my outside temperature sensor I had issues w AC bc the car would sensor -40 and would not start the AC..... u could start from that... and/or go to mechanic who has laptop w software that could erase all errors... that helped my steering.... I changed the steering pump myself and it would work much better however not as it supposed to... but after erasing all the errors it start working like brand new;)
 

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was wondering, how do you jump the compressor to see if its working? really dont wanna replace the compressor if i dont have to and im running out of ideas
 

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was wondering, how do you jump the compressor to see if its working? really dont wanna replace the compressor if i dont have to and im running out of ideas
there is a cable on the compressor with a jack, you need to connect it with a positive source. Make sure you connect the positive terminal not the ground one.
What year is your 740. Do you have a pressure reading on the low side or the high side?
 

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its a 98, as far as the pressure, on the low side it reads just a shade over 65 psi, on the high side i have no clue....k now im gonna sound really dumb here but where about is the "jack" located on the compressor
 

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ok i got the compressor to engage (by jumping it), a/c blows cold air.....unhook the jumper wire and the compressor shuts off.....when unhooking the jumper wire from the compressor noticed the a/c coolant lines were both very hot, i remember seeing somebody else having the same problem in another post not sure where tho, im assuming they were hot because the aux fan didnt kick on because it was jumped, i dunno justa guess....
 
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