Trying to figure out how to jump start AC Compressor Clutch on 1992 850i

[OldDuck]

Hey guys!
I'm a new owner of a 1992 BMW 850i. I have done a lot of research on this car and so far have fixed/done a few things to it thanks to guides on this forum.

There's still one thing wrong with the car, which is the AC. It doesn't blow cold air, but the heater works fine. I tried following Tim's guide on how to recharge R134a (this car AC system has been converted from R12 to R134a),
but the AC compressor clutch does not engaged when the AC is turned on. The AUX fan turns on when the snowflake light in the car is on. It appears the gas in the system is low when I attempted to recharge it. I also tried the broomstick handle thing, and that didn't do anything either.

So I have done some research and my understanding is you have to jump start AC compressor clutch in order to charge low gas AC system. I pulled the plug from AC compressor and it appears to have 3 wires, and this is where I need you guys help...
I don't know which wire I have to jump to positive terminal and which wire I have to connect to the ground... Most guides I see out there only have 2 wires and not 3 like this one...

1st wire: black/white
2nd wire: blue/red
3rd wire: light blue



If any of you know how to jump start this thing, please show me the way.

[Stantz]

I don’t know which wires are what, but somewhere is this huge manual lies the answer:
https://www.meeknet.co.uk/E31/e31_92.pdf

You’re looking for which wire supplies the 12V to engage the clutch.
Hope that helps.

[cartoonz]

the only way to do this properly is to use an actual AC machine and pull a vacuum, THEN refill it with 2lbs of R134a
You do not need to "jumpstart" anything.

Your compressor could be bad, or F29 fuse in the front fuse box (7.5a) could be blown, The pressure switch itself could be bad or have a bad connection too.

That said, if you are bound and determined to test the AC clutch, put 12v+ the Black w/grey stripe wire at pin #1

[OldDuck]

Thank you guys for the answers! Now I have some lead on where to go from here.

First, I will pull a vacuum from the system to see if there's a leak in the system. Then test the AC compressor clutch by providing 12v+ to black w/grey stripe wire.
And take it to the shop to have it recharge with the AC machine if there's no leak and if the compressor kicks on.

I already checked the fuse and it was still good. As for the pressure switch, I don't know how to test that, so I will probably let the guy at the shop do it.

[cartoonz]

you need the AC machine to pull the vacuum anyway... just take it in

[OldDuck]

ok, I think I found the problem. There was no leak or anything after I did the vacuum test, so I attempted to jump start the compressor and it doesn't turn on.
The compressor is definitely gone...

Time to follow the guide from this thread: https://www.bimmerforums.com/forum/s...AC-lock-sensor

Thanks again for the help.

[rjjablo]

Replace the Compressor, receiver dryer, the PIA item behind the dash. Make sure you inspect the evaporator also. If you have an original R12 compressor you need the new bracket also. Make sure you flush the condensor. Have fun

[OldDuck]

Replace the Compressor, receiver dryer, the PIA item behind the dash. Make sure you inspect the evaporator also. If you have an original R12 compressor you need the new bracket also. Make sure you flush the condensor. Have fun

I think I got all the parts I needed including the new bracket for this job, except the item you mentioned behind the dash.

Any idea what it's called?

[cartoonz]

The new Denso compressors are the way to go, I wrote the complete guide for bypassing the lock here: https://www.bimmerforums.com/forum/s...re-compressors

Now, some will kick and scream... but... especially if you have not had components pulled from the AC system for extended free air time, you really don't "have to" replace stuff under the dash, etc... replacing the dryer is smart - but even that can often be skipped in a pinch.

[rjjablo]

Expansion Valve And I got the big kit of O-Rings because you will come up short

[mlytle]

There is no "jump start" for an ac compressor. Adding 12v to the compressor wire does not test the functionality of the compressor. All it does is test the clutch on the pulley than drives the compressor.

[cartoonz]

There is no "jump start" for an ac compressor. Adding 12v to the compressor wire does not test the functionality of the compressor. All it does is test the clutch on the pulley than drives the compressor.

Which is exactly what he wanted to test.

[OldDuck]

Hi guys,
just want to give a quick update on what was wrong with the AC system after weeks trying to find out what was wrong with it.


Turns out it was a broken connector by high AC pressure switch and that was it...
After I jumped the wires to bypass the lock sensor by cartoonz's guide and replaced the compressor to single wire, the compressor would turn on maybe 1 out of 10 tries and then cut off after a couple seconds, so that's when I started to think it could be wiring issue somewhere...


I believe the previous owner tried to fix this issue before as well, but he couldn't figure it out and that's why he sold the car.


As for ac compressor, I didn't use denso one like most people on here do. I went with UAC CO22016C as I was able to get a good deal on it for only $100.
The diameter of the pulley matched the size of the old one exactly and I didn't have to change the belt size.


Also here are some pictures of where you have to jump the wires. I figure it might help some people out as I wasn't sure if I got the right one when I did it. lol

20210204_133233_HDR.jpg
20210204_134215.jpg


Thanks again everyone for the help! There are some stuff that I still need to work on this car, so if I don't see the guide on here for stuff that I'm going to do, I will try to post on this forum and try to contribute.

[clockwork]

F29 fuse in the front fuse box (7.5a) could be blown

Hey Cartoonz, I keep blowing fuse 29. Would you think the compressor keeps blowing it? It only blows when I play with the A/C HVAC system, but sadly, everything else tied to the fuse suffers when it blows, BUT nothing else connected to that fuse causes it to blow...

[cartoonz]

Hey Cartoonz, I keep blowing fuse 29. Would you think the compressor keeps blowing it? It only blows when I play with the A/C HVAC system, but sadly, everything else tied to the fuse suffers when it blows, BUT nothing else connected to that fuse causes it to blow...

that's probably your $100 compressor... sorry

[OldDuck]

that's probably your $100 compressor... sorry

My ac compressor is still kicking! I will report back if it failed within a year tho.
For now, it blows nice cold air.


As for clockwork's issue, maybe a short somewhere? I would check the wires and connections.

or maybe the clutch is failing and popping the fuse.

[cartoonz]

oooff... my bad... @Clockwork - there are a whole lot of things fed by F29, and several are IHKA AirCon related.
e31_91 (2020_01_17 18_07_48 UTC) (2021_02_05 23_59_48 UTC) 46.jpg
Compressor relays / cut off relays / fan relays would be suspect. Also, if you did the Compressor Lock Sensor mod I wrote about earlier, make sure you got the correct wires.

[ChrisFuture8]

Mike, I haven't read the entirety of the thread, but wanted to say that when I first bought my car, fuse #29 was blowing all the time and to rub salt to the injury, I was also only getting hot air to the footwell every time I need to get some cool air going. An 8 gathering was fun but brutal needless to say.

Anyways, the cause on my car for the #29 fuse issue was the clutch had gone kaput on the a/c compressor. Took that out and had it rebuilt and no more blown fuse.
I knew it was a bad a/c compressor clutch because of the sound it made (like a jack hammer under the hood) every time I turned on the a/c.

[clockwork]

oooff... my bad... @Clockwork - there are a whole lot of things fed by F29, and several are IHKA AirCon related.
e31_91 (2020_01_17 18_07_48 UTC) (2021_02_05 23_59_48 UTC) 46.jpg
Compressor relays / cut off relays / fan relays would be suspect. Also, if you did the Compressor Lock Sensor mod I wrote about earlier, make sure you got the correct wires.

Thanks Cartoonz, I have never replaced anything in my system besides the R134a just 2 summers ago.

I never hear a sound from engine bay that sounds bad or especially like a jack hammer. Yikes. That must be a scary sound to hear in an engine bay.

I will look more into this issue in a few weeks with connections first.

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