appreciated previous response. Knowing a bit more now I notice the following:
- a/c clutch engages and stays engaged

- the 'fuel-economy-gauge' suggests that there _is_ a load on the engine. One can also hear rpm change a bit etc. when engaging a/c

- climate control appears to work (blower, vent changes, etc) except the air coming out isn't cold.

- fuses are OK

- failure of a/c wasn't slow but occured
between turning car off at night and starting again in the morning.

- very puzzled, guenter. any help appreciated!

p.s. Is a sruck valve reasonable? do I then need to rebuild the compressor?

Have some one to check it have enough freon in the system or could be the expension valve
Check the heater valve is working correctly? ?

For what it's worth, I have a 420 SEL where ac seemed to work fine but the air getting warmer and warmer. I've had the car for 2 months, and noticed that there was oil on the lines leading from the condensor (the grill like component attached to the front of the radiator). Took it a shop, they vaccumed the lines and refilled with oxegen then checked for leaks. Sure enough, the rubber line leading from the condensor to the dryer had a leak. Line cost $27, will cost about $175 to have it installed then recharged with freon. In my case, as the freon leaked out the system got warmer. Maybe your's leaked overnite. Just a thought. Good luck!

Be sure the system is fully charged...
Have the Mono heat valve checked to be sure it isn't letting any hot water into the heater core.

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Benzmac:
ASE CERTIFIED MASTER AUTO TECHNICIAN
LEAD TECHNICIAN FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM