E34 A/C Always on

[Frank87]

Car: 530iA V8 Sedan (12/1993 Euro) & 525i (M50) Touring (1995 Euro)
A/C Type: Manual A/C

I have searched on this forums and other forums. I came across a post on this forum where someone has the exact same problem. However, the link provided there to a possible solution no longer works.

Problem: After starting the car, the A/C turns on and stays on. No control or led from the A/C button or AUC button.
I thoroughly overhauled the A/C system since I bought the car cheap with a boken A/C compressor.

I have replaced:
- Dryer
- A/C Compressor
- A/C Condensor
- All small O-rings at junctions and metal hose adapters

After that, I put 1200 PSI Nitrogen on the A/C system. After 45 minutes, it still had 1200 PSI. I consider the system to be sealed.
I then vacuumed and filled the system with 1550Kg R134 including PAG oil. The system now cools excellent. But it won't turn itself off.

I then:
- Changed the microfilter and took the black A/C computer with 3 sockets out. Carefully cleaned that computer with compressed air (low BAR).
- Used socketcleaner on the sockets and connectors to abolish any interference from grime
- Plugged the computer back in.

Now, when I plug the computer back in. I am able to use the A/C and AUC buttons. The green LED lights up! However, after starting the car, it takes about 10 seconds before the buttons no longer respond. Although the buttons can be pushed in the beginning. The A/C compressor won't respond.

I then:
- Checked relays. Switched A/C relay with identical horn relay without any result
- Checked for any fault codes, no codes
- Checked the functioning of the needle in the evaporator by laptop, it measures temperature (I guess it does so correctly.. always between 3 and 8 degrees celsius)



So, unless the computer from the wrecker was also busted, I do not know where to continue this operation. Any ideas / suggestions? Again, the system runs great.. but won't shut off.

[632 Regal]

I had one where the AC compressor clutch would stick but doesn't sound like your issue.

Now, when I plug the computer back in. I am able to use the A/C and AUC buttons. The green LED lights up! However, after starting the car, it takes about 10 seconds before the buttons no longer respond. Although the buttons can be pushed in the beginning. The A/C compressor won't respond.

Does the green light still go on and off?

Did you try and remove the fuse and see if it shuts off?

There is also an outside temperature sensor and a heater core temperature sensor that could be faulty adding to the fun.

Welcome to the forum!

[Frank87]

- Green LED no longer functions when the buttons are blocked out
- Did not test with fuse removed but checked all fuses and they check out ok. Will test with removed fuse
- Will test the other 2 sensors but this still does not explain why I cant manually control the AC

[632 Regal]

- Will test the other 2 sensors but this still does not explain why I cant manually control the AC

Yes real strange. The sensors might be getting stuck? Trying to narrow in on the issue.

[Frank87]

Update:

- Installed an A/C computer from another wrecker (the black box with 3 sockets near the cabin filter)
- Replaced the evaporator temperature sensor (On the right side of the pedals right behind 1 cover)

All ok now. The first computer from the wrecker was probably busted.

[632 Regal]

Success! Glad to hear it.

[Frank87]

Update:
The exact same problem appeared again. The compressor will turn on a few seconds after the car has been started.

Pulled the codes from the car. Nothing special on the A/C system. I can only shut down the compressor if I:
- Remove the compressor relay
- Remove fuse 9 and/or 29. Both 9 and 29 shut down the compressor- Unplug the compressor (duh)

I have:
- Replaced the A/C computer (wide black box with 3 sockets) with one I know is working (working wrecker)
- Checked the evaporator sensor with OBD equipment. Works and gives correct temperature readouts

For some reason, I think the A/C computer I thought was busted a while ago, wasn't busted at all. I now have 4 A/C computers here. 1 may be busted but the other 3 work 100%. All tested by the guys who supply and who are trustworthy (no cure no pay).

I have no idea where to look... I get no codes and the components of the A/C system are ok. I have the regular IHKR manual A/C.

[shogun]

I guess you know that the AC is automatically also on when the AUC is on, no need to to push the AC button then?

[Frank87]

I know that and I have AUC. The thing is, once the car knows something is wrong, the * and AUC buttons no longer respond. I can't even control the AUC or recirculate mode.

When I disconnect and reconnect the IHKR computer, it shortly responds with leds when pushing the buttons. No matter what I push however, it does not give me control over the compressor. I CAN use the recirculate button at that time.. but only for about 5 minutes before I can no longer control the 3 buttons. Somehow, the car or a system knows something is wrong.

[whiskychaser]

The IHKR doesn't directly control the compressor - the DME does. Fuses 9 and 29 provide the trigger and main supply voltage to the compressor relay but it will only be thrown if the DME grounds the trigger side. Or something else does - maybe a short to ground?