Hey mate,
Unsure if you have had this fixed or not but I thought I might share my experience with my M140i Air Conditioning not working, similar to how you described.
I noticed my AC not blowing very cold air one Summer day (+30C outside air).
Next day not working at all.
Day after that working a little bit, as it was cool but not cold with the AC set to minimum temperature.
I got a local Air Condition guy to check the gas as I was thought I might have a refrigerant leak. He checked and it refrigerant gas levels/pressures were ok.
Next, with the test equipment still attached, we started the engine to check what the pressures in the AC lines were doing when the motor was running and AC compressor spinning. We noticed the pressure climbing and climbing until the AC compressor eventually cut out to save itself from over pressurizing. This is an indication that the refrigerant gas in not being cooled effectively. This is when the AC guy said I’d need to go to BMW as he said it was too complicated of a system for him to fix. I decided to look deeper and see what I could find out before going to BMW.
The M140i Air Conditioning is not like conventional Air Conditioning systems. They use coolant and a small electric water pump to cool the refrigerant gas so the AC system can work as required. Sometimes this is called the Low Temp cooling system. However, this coolant and water pump are not the same system as the one used to keep the engine cool, and do not interact with each other.
It is a separate circuit, which also is linked to the Air-To-Water turbo intercooler that lives in the intake manifold. Meaning, if there are issues with this cooling circuit, the air intake temperatures for the motor are also affected. Likely the motor will be running a little down on power as it will have to compensate for the higher air intake temperature.
I checked for any fault codes using my BM3 app and the only error code was relating to a ‘Coolant Pump Run Dry’ error…
Under you bonnet you have two coolant caps on the right hand side. Larger one for engine coolant, smaller one for the Low Temp cooling system. I checked the coolant level of the Low Temp cooling system, and I found mine to look completely empty. Yours may be the same. I added about 1-1.5L of coolant to that reservoir and carried out a simple system bleed with the cap still off.
Great how to guide:
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Doing this got the AC to work again. I suspect that if there is an issue with your Low Temp cooling system water pump, you will find out doing this test as you wont hear the sound of the water pump running or see coolant movement/bubbles in the reservoir.
Now my attention turned to why it was low on coolant. Turns out the radiator for this Low Temp circuit is right at the front of the car with little to no protection. At some point while driving, a rock had hit this radiator, and a very small leak had started. So small that it only shows up when the system gets hot and under pressure. Once I found this, I drained the Low Temp coolant system, removed the bumper to access the radiator and managed to patch the tiny hole with some metal putty. Refitted everything and refilled the Low Temp cooling system, then carried out the bleed procedure a few times until the level in the reservoir stabilized. It’s been almost 12 months now, and this fix has held up.
In summary: AC gas was overheating and shutting the AC compressor down due to a cooling system leak on the Low Temp cooling circuit, causing the AC to not work effectively 99% of the time.
I hope this gives you a few things you can check yourself, and you can fix it up easy enough like I did.
Good Luck!
Edit: Formatting