Mercedes-Benz W220 air conditioning blows hot air on one side
S400320 CDI400 CDI
Why does the W220 air conditioning blow hot air only on one side?
A common cause is the heater core control valves, known as the "balls" or "ram's eggs". When a valve sticks, hot coolant reaches one side of the heater core even though the temperature is set to cold.
How can a stuck heater valve be fixed?
The valves are in the trough at the bottom edge of the windscreen, and they can be reached by removing the wiper arms and the plastic cover. A stuck valve can be freed by tapping or moving it. A removed valve is cleaned, because dirt or debris can stop it from closing.
Does recharging the air conditioning fix the hot-side fault?
Usually not. The heater core and the air conditioning are separate circuits, so topping up the refrigerant does not affect the valves sticking.
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