The climate controls in my car (2013 GL450) started to randomly change to different modes. Sometimes you’re able to select modes (Off, Auto, AC, etc.), and the system functions properly. Other times, the buttons don’t work, and there are no lights on. When the lights are off, it will randomly change modes, and the blower will erratically switch from low to high, then back to low. Then the lights will come back on, and you can control the system, and components seem to respond accordingly. It constantly goes through this cycle.

I have done the following troubleshooting, based on internet searches:

Climate Control Module – This seemed like the most reasonable solution. I purchased a module off eBay, from a wrecked car. I installed it, and It shows the exact same symptoms.

Fan Control Module - I don’t believe it’s the fan module, because it is responding to the signals from the climate controls when it gets them.

Battery – I tested the battery. It said good, but needs charged. I charged the battery and retested to make sure it was good. I am still having the same issue.

ECU – The only code I get is “Communication with the air conditioning has a malfunction”. This goes away when the climate module has power. If it was the ECU, I’m guessing I’d get more codes.

Fuses – I checked the fuse (19), and it was fine. Are there other fuses? I’m guessing if it was a fuse, the issue wouldn’t be sporadic. I did pull the fuse, hoping to just disable the system. When I do this, the engine fan runs all the time. I read that this is a common response when it losses signal.

AC DTC – I have the following DTC under the AC: “The power supply to the LIN bus subscribers has a malfunction. The limit value for current has been exceeded”. I don’t know what this means and haven’t been successful in searching these codes.

Any help would be appreciated. I have an appointment at the dealer, but they couldn’t get me in until later this week.