First off, I apologize if this issue has been addressed before. I searched before posting but I did not find any solution pertaining to my situation. 
I have a 2016 Mercedes-Benz GLC 300 with 47K miles, it worked quiet and nice since I got it in 10/2020. I am located in the Caribbean but imported it from Florida. About 2 weeks ago I noticed the engine noise at idle was extremely loud, I looked and realized that the loudness is coming from the radiator fan. It’s so loud that it sounds like a diesel truck. This only happens when the AC is turned on. There are no MIL on the dash and everything still works fine. AC still very cold and the vehicle still performs normal when driving in all modes. Only issue is the loudness of the fan. I scanned it using my icarsoft MB 2 but no codes. Can anyone help, please. I’m on an island with no MB dealerships and don’t trust the local self taught mechanics to go in there. The noise is very loud and embarrassing. 😔



When you turn the AC on, it puts an additional load on the engine, because it now needs to run the air conditioning system.  When that happens, the radiator fan turns on to keep the motor cool due to the additional load it needs to deal with.  Your car is probably fine.

Thanks for responding Jonah, whilst I want the car to be fine this load was always being placed on the engine from prior AC use at which point the fan worked very quietly until now and the noise I’m referring to is new. 

Okay.  Are you sure it is just the radiator fan? Newer glc300s also have a fan to cool down the MBUX display unit, and that fan can also be extremely loud when it kicks in.  Apparently the MBUX unit is too close to the motor, and the cooling fan has 3 speeds, so when it kicks on it can be extremely loud.  That might also be the issue you are having, but the MBUX unit is fine; its just the fan making noise.  

Yes I’m certain it’s the radiator fan. During normal operation it does not get loud but as soon as the AC is on it gets extremely loud. Louder than it used to, also I don’t think I have MBUX. I have a 2016 GLC, also once the AC is turned off the loud fan slowly gets back to normal. Now I understand the fan supposed to get louder when the AC is turned on but not this loud and if it’s normal then why didn’t it be so loud from the time I got the car. I just bought a new fan and I’m receiving it this week. Paid $1100 and I’m still not sure if it’s a fan problem or something else. But I need it back to normal so bad that I purchased a new fan from MB. 

It seems that the fan is running full speed as soon as the A/C is turned on. Have you checked the plug or wires or the temperature sensor for the condenser?