BMW Z4 AC Failure: Compressor Warning Signs & Diagnosis

Hey there! I have some experience working on cars, nothing too advanced though. I actually dealt with something really similar on my 2012 BMW 335i last summer. The AC symptoms were exactly the same, no cooling, wouldn't engage, warning light, the works. Took it to my regular workshop and turns out the AC control unit was completely fried. They diagnosed it properly and replaced the unit, cost me about 980 Euro total, including labor. Car's been running perfectly fine since then. Before I share more specifics about what exactly they did to fix it, could you tell me what error code you're getting? Also, have you noticed any other electrical issues? This could help narrow things down, as these BMWs can be a bit tricky with their electronics. For what it's worth, it might not be the compressor, could be the control unit like in my case. Best to get it properly diagnosed before replacing parts.

Thanks for sharing your experience! My mileage is at 140890 KM and I just had the regular service done last month. I'm getting error code P0645 and no other electrical issues that I can notice. The AC just suddenly stopped working during a drive. Really hoping it's just the control unit like in your case and not the compressor, as I've heard those repairs can get pretty expensive on these models. Did your mechanic mention anything about common AC failures in these cars?

Oh hey again! Yeah, that P0645 code is actually exactly what I had, it's related to the AC compressor clutch circuit. When my mechanic walked me through it, he mentioned this is pretty common in these BMW models around the 130-150K km mark. In my case, they first thought it was the compressor too, but after testing the circuit they found the control unit wasn't sending the proper signal to engage the compressor clutch. The fact that you're not having any other electrical issues is actually a good sign, same as my situation. Since you just had regular service done, I doubt it's a maintenance-related issue. My mechanic told me these control units tend to fail due to heat stress over time. When they replaced mine, they also added some extra heat shielding to prevent the same issue from happening again. I'd suggest getting it checked soon though, running without AC is no fun, and I learned that leaving it too long can sometimes lead to bigger problems. The good news is that if it is the control unit like mine, it's a much cheaper fix than replacing the whole compressor. Let me know what you find out when you get it checked. Really curious if it turns out to be the same issue!

Thanks so much for the detailed follow-up! That's actually really reassuring to hear that you had the exact same error code and it turned out to be just the control unit. I've booked it in at my local BMW specialist for next week, and I'll definitely ask them about the heat shielding you mentioned, sounds like a smart preventive measure. I was getting pretty worried about the potential cost if it turned out to be the compressor, so this gives me hope it might be a more manageable repair. Really appreciate you taking the time to share all this info. I'll make sure to update once I get the diagnosis, but feeling much better about it now. Good to know it's a common issue around this mileage too, makes me feel like I'm not just unlucky! Thanks again for all your help with this! Fingers crossed it's a straightforward fix like yours was.