1995 BMW M3 A/C Issue.

[JROM3]

Hello Everyone,

I have a A/c issue that I just can not fix! I have a 1995 BMW M3 S50, that is tuned by RK tunes and simple bolt ons. A/c compressor engages and blows cold when 12v source is ran directly to it. I changed the two big yellow relays with brand new oem ones. I changed the Climate control unit and still no engaging. The snow flake turns on but doesnt kick on the A/c. I tested for continuity from the compressor to the relay and thats fine. I jump the relay and the compressor kicks on! Im thinking there is a signal issue between the snowflake button and the relay. Can it be ECU related? or is there any other sensor that need to be check ok so that the DME can send the signal to the relay to switch on? Would like some guidance on fixing this before getting shafted at the local BMW dealer!

Much appreciated!

[AJLM34A]

http://wedophones.com/Manuals/BMW/1995%20BMW%20318i-s-c%20-%20320i%20-%20325i-s-c%20%20Electrical%20Troubleshooting%20Manual.pdf

Go to the IHKR/climate control section

[bmwdirtracer]

Welcome to the forum, Jerome.

There's a lot more involved than turning on the switch. If you study the wiring diagrams linked by AJLM34A, above, you'll see that the system is complex. The DME (engine computer) actually turns on the compressor, via the compressor control relay. The DME will want to see correct readings from the pressure sensors, temp sensors, etc. The first step would be to evacuate, then refill the system with EXACTLY the correct amount of R134a. This requires a professional a/c machine.