Cabin temp way too hot in 2015 E400
 

Hi All,

Weird issue only noticed in my new to me x 4 month E400 wagon (CPO)
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Now that the weather is cooler I am finding need for the heat. When I have the auto climate control set to say 21 degrees (Celsius) it is making the cabin quite hot. I have to set it to 16 or 17 to be tolerable.
Noticed if I turn the temp setting right down to LOW, it starts blasting HOT air. Air is so hot that the vents can be hot to the touch in the dash lol, like being close to a space heater.
When I press the AC REST button it just blinks, can't actually turn on the AC.

I assume something is wrong here with the system but wanted to see if anyone else had experienced it before I book a service.

I know the older Mercedes models used a REST feature so that you could circulate warm or cool air after the engine was off for up to 30 minutes. My 2011 doesn't have a REST button, but it does have a button to turn on and off the AC compressor.


https://cimg0.ibsrv.net/gimg/www.mbw...3ea8ecc19f.jpg

Hot air when climate is set to Low. That should be cool air. Something is very wrong.

Have the system scanned. There are actually several temperature sensors in the cabin. Could be a bad sensor or some blend valve. Hopefully it should be covered by the CPO warranty, otherwise there's always that $150 off $300 coupon mentioned elsewhere.

Be sure all of your air vents are open. It is possible that you are creating a situation where the cabin temperature is uneven - hot where you are and maybe cold where a sensor is located. It will then try to fry that cold sensor until it is warm, in the process baking you.

Just a guess. I've had other cars do that. My wife often turns off the passenger-side vents, which sometimes gave strange climate control performance on the driver's side.

Do we have the same wife? Mine does that all the time, hot or cold. Drives me crazy. Thought the car's HVAC controls were dead until I figured out her habits.

Thanks guys. All vents are open. What is odd is I can't even activate the AC compressor if I want to, so I think something is wrong.
Have a service appointment booked....
Incidentally the engine runs at a high-normal temp - around 100 -- other people find that with this engine?

What do you mean by can't activate the compressor? I believe MB and many other manufacturers now use variable displacement compressors so there's no A/C clutch like in the past.

When I press the AC button it just blinks and doesn't turn on -- and on the COMAND screen when I make any temp adjustment it says "AC OFF"

There's something amiss there. The light should stay on, and of course, the COMAND message is unusual, too.

As for operating temp, mine runs around 85-90 C when fully warmed up. I've never seen it any higher, even in summer with the air conditioning on.

I had a car do this once (non Mercedes) - the engine cooling fan had gone out. It would not allow the car to turn on the AC compressor to reduce engine heat. My money is on something along those lines. Keep us posted.

Ends up you were correct - the temp sensor in the overhead console was misreading the cabin temp at -50 Celsius at all times, and so would not even let the AC compressor activate when I asked it to. Sensor was replaced and all working fine now; covered under CPO.