Mercedes: 380sl AC, climate control system, engine thermostat

Question
My AC was working, now its intermittent. On-Off. Should AC blow thru all vents? And now the engine seems to overheat...A mechanic said I would need new fan for the reason my ac is not working. which fan are they referring to?

Answer
Mike,
The climate control system depends of the temperature of the heater core or the evaporator to determine when to bring on the fan.
This procedure keeps you from getting blaster with freezing air before the engine temperature has risen enough to open the thermostat to allow water to enter the heater core. Once the core temperature come up then the climate control bring up the blower speed. There is an air temperature sensor over the passenger visor that send air over the interior air sensor.
As the air in the passenger compartment adjusts to the control set then the fan speed is spooled back to cut down on the air noise. All this is determined when you press the fan control button. You can override it by pressing the full speed button. If you have the air split control pressed the AC is activated then the dash heat is passed through the evaporator to remove the moisture to keep the wind shield from fogging up.
When you set the thermostat to blue, then the AC is brought on line and the hot air is limited by the monovalve which controls water to the heater core.
If your radiator fan thermostat is defective then the motor will show an overheat condition, because the fan need to operate to remove heat from the radiator. The block water sensor determines how often or if the fans are needed to dissipate heat.
If you have duel electric fans, they would probably both operate full time when the AC is activated.  This action helps remove the heat that is distributed to the condenser in front of the radiator by the AC unit. You are actually removing interior air to the Condenser.
If your fan are not working or working intermittently then that would effect the action of your climate control system.
Also, if you have an engine thermostat sticking that will cause the engine to overheat as well. But, this would be independent of what happens while the AC is operating.
Good luck. Let us know what you find out.
Rob