B. A.

I am driving 2015 Mercedes C400 w205.
This morning I realized that the AC is not blowing cold air. I assumed that it was because it needs refill and I was about to wait until Monday to have it refilled.

Then in the evening, when it was really calm, I started the engine, and I heard extremely loud fan sound from the front of the car. I guess it is the Engine Cooling system(or what it could be? comes from the grill). Sounds like the fans are running at highest possible speed and almost sounds like a jet. Starts 5 seconds after starting up the engine, and I drove around 7-8 minutes and the fans were still running at max speed(meanwhile AC is off). So I shut down the car.

There are no errors on the dashboard, and the engine temperature is normal as always.

What could be the problem? Are those two related? Could a simple refill solve the problem? Or is there something more serious?

bzammitt

My C400 won’t blow cold A/C about 1/10 times after sitting in the sun all day. Haven’t tracked it down yet since I don’t have warranty. I’ve heard it might be a software update that could fix the issue. I think it’s a bad sensor or controller that malfunctions when too hot. Regarding the jet fan, my car does that too. I think there’s probably just a higher and lower setting for the radiator fan. Let me know if you fix your A/C issue with a recharge!

B. A.

Sure! Sounds familiar, because today I left the car in the sun(approximately 30*C or around 86*F) all day, and then the AC didnt work.
Is your Engine Cooling Fan also this loud when your engine is running? I have never paid to attention before, but this afternoon it literally sounds like a jet!

bzammitt

Not always, only on the super hot days or if it’s running and not moving for a while!

B. A.

Interesting. I will pay attention to that, and I will keep this post updated. Thank you for your reply though! It helped me a lot.

ItalianJoe1

Have the car scanned for faults. Most likely there is something in the cooling system unhappy, if the temps are super high (or the car falsely thinks they are) it will disable the A/C, so if you find out what is causing the fan to be at max you will probably get your A/C back.

B. A.

So today I went to a car service and have checked the car for faults. There was an error with the Air Pressure Sensor(if I remember correctly) that measures the pressure inside the A/C. It was defect and wasn't working, preventing from the big fan(the radiator) to communicate with the pressure inside.
So, since the car doesn't have the pressure data, instead of disabling the main radiator fan, it puts up into high(the max), or as the mechanic described "If the radiator has no data, it will just do its best *just in case*, instead of completely shutting it down.".
Sensors itself costs arounf €50, so it was a cheap repair.

B. A.

True. That was the case(almost). The car had basically no data, so it ran the radiator to max *just in case*

bzammitt

That’s good to hear! Did you bring it to Mercedes or a local Indy? Do you have the invoice that shows the part number? Do you know where the part is located in the car? Sorry for all the questions lol but I bet that’s what’s wrong with my car too

bzammitt

Part number?