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Q: Air Conditioning on 2000 Mercedes-Benz SLK230

When turning on my air conditioning, I only get hot air out of the passenger vents. On the driver's side, the air is cold. Is there a special combination of setting on the a/c controls I can use to match both sides so that cold air emits from all vents?
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The problem is most likely the 'duo valve' which controls the flow of hot coolant to the driver/passenger side. these valves are actuated through solenoids. On mine, one of the solenoids had burned through resulting in exactly the same problem as you have (cold driver, hot passenger). The valve is found under the hood ahead of the electronics boxes (looks like two small metal cans), you can't really miss them. Pull the connector and check the following: measure the resistance over the connectors for each of the solenoids (measure between the center pin and each of the outer pins), if the resistance between either center pin / outer pin combination is not about 10-25 Ohm, the solenoid is bad. If these are good, turn on the car and measure the voltages in the connector (again between center pin and each of the outer). Do this with the temp control on max high and max low. In the one case you should see 0V, in the other more than 10V (can't remember if hot is 10V or cold is, but you will see the difference). If this is not the case, the controls are bad. Now for a bad solenoid, the easiest fix is to remove the solenoids by removing the 5 screws holding them in place and go to a breaker yard and get the solenoids of a C-class (Mercedes only sells the entire valve assembly and the ones for an SLK are really expensive while most C-class cars have exactly the same solenoids).
If the checks above didn't work, it might even be simpler, take the entire valve assembly apart and clean it as the valves themselves get stuck every once in a while.
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