Hi everyone,

I’m having a strange issue with the air conditioning on my 2007 Mercedes W221 S320 CDI.

The A/C works only intermittently. Most of the time it either blows warm air or doesn’t seem to cool at all.

Some symptoms:

* Sometimes the A/C suddenly starts working when the engine reaches around 3,500 RPM, but then it may stop working again shortly afterwards.
* Occasionally it starts working while driving without me touching any settings.
* When it does start working, sometimes it stays on for a long time, while other times it only works briefly before stopping again.
* There was one occasion when the A/C was working and I turned the temperature to maximum heat, but it continued blowing cold air (just with weaker airflow).
* I’ve noticed that if I leave the temperature set to the minimum (LO), the A/C sometimes continues working. However, if I increase the temperature even slightly, the A/C may stop working completely.
* Sometimes the airflow is present but the air is warm instead of cold.
* Other times it feels like the system is barely blowing at all.

Has anyone experienced similar symptoms on a W221?

 

Any codes?

Sounds like it needs regarding as the first port of call. But reading the codes will confirm this.

 

AC Kompressor (solenoid valve) is a culprit

 

low gas
or
comand updated and compressor not re-enabled

 

This. The solenoid sticks and you get wonky intermittent air. Happened in my W212. Bought this solenoid:



Don't know if it's the same part for the 221 compressor but that would be where I would start. I didn't end up replacing it because after some regular use my system started behaving properly and it's been fine ever since. I think mine was sticky because the car sat for so long before I bought it. It sits on the shelf until my number is called.

 

Need to use a Mercedes specific OBD scan tool to diagnose.

- Check for any fault codes that point to the issue.
- Read evaporator temperature, see if it is in fact getting cold.
- See refrigerant pressure at condenser. You should see the presure increase with the ac turned on.

Use a refrigerant refill hose w/gauge to see low pressure. I'm not sure a scan tool will show low pressure side.

- Check low pressure with ac off. Then check pressure with ac on. On a warm day you should see the pressure fall, usually to green marking on standard refrigerant gauge.

You dont mention any lights blinking on the climate control which is good. The ac button light will blink if theres an issue usually.

The compressor could be functioning but if there is not enough refrigerant the evaporator cannot cool down the air passing over it from the blower.

Without a scan tool a simple way to check if you need to top off the refrigerant is connect the refrigerant hose w/gauge to the low pressure port. Warm day it should be reading 50 + psi. Now turn the AC on, if the gauge drops to zero or hardly any you should add a little refrigerant. If the gauge does not move from the first reading further diagnosis is needed.

My AC was blowing hot air when turned on. I connected the hose w/gauge and saw the pressure was low from where it should be on a warm day:




I turned the AC on and the pressure tanked:




This told me at least the compressor is working. I added straight refrigerant, no stop leak stuff, until the gauge was showing around 36 psi.





Air coming out the vents was nice and cold again. I also had my scan tool to see the evaporator temperature was getting very cold. Before adding the refrigerant the evaporator temperature stayed hot.

 

Your symptoms are exactly what I was experiencing with my 212. I just uploaded this video for you. Check it out and try doing what i did in my video and see if you can bust loose the sticky control valve. I started the video with the valve stuck -no AC- then revved it to un-stick it and had proper AC. If yours behaves like it did in my video, I would be fairly certain of the faulty valve. Nice to have a good gauge set too. This "analog" testing can get you pretty close to the problem if you can get your hands on a set of gauges but don't have access to STAR or another appropriate scanning device right away. This was February in Florida but it was still near 80 degrees F so warm enough for a good test. The pressures on my gauges after the control valve broke loose are the appropriate pressures for my ambient environment in terms of heat and humidity.