Ok, Here goes.
I have a 2000 S500, I let the vehicle sit for about 3 months. The battery drained all the way down. I removed and fully charged the battery, and re-installed.
The A/C does not work now, only warm air. Upon checking the compressor is running and the condensor is not got hot/compressed gas to it. the line after the filter/dryer is cool. Hmm. also appears to be a electric switch/valve on the orifice bracket on top of the filter dryer.
While doing this, I noticed that the electric cooling fan was not running, and the engine was at normal operating temps.
My thoughts were, this all makes sence with the A/C, if the cooling fan is not working then the system will not let the A/C operate normally. Trouble shoot the fan motor, the motor works properly. No voltage to the motor. Check for fuses, none blown. Passenger front seat area, below floor pan. Power out at all positions, ie: those fuses are good.
Where do I check next?
Thanks.

 

I was told yesterday, that the relay will not turn the fan on until the coolant temp gets to about 228 or between 225 and 230. That seems a bit high to me?
So, what is the temp that switches on the cooling fan?

 

Check your coolant level. Sounds like the coolant temp switch is the culprit.

http://www.justanswer.com/mercedes/2...ked-power.html

HowStuffWorks "How Car Cooling Systems Work"