Why is my AC cold on one side only?

Cold on driver side but warm on passenger (or the reverse) is almost always a blend door actuator problem on the warm side. Dual-zone climate control uses a small electric motor to swing a door that mixes cold evaporator air with hot heater-core air; when the motor fails, that door stops moving and the affected side gets stuck full-heat or full-cold. You'll often hear a repetitive clicking from behind the dash. Refrigerant is not the issue — a shop can confirm by scanning the HVAC module for actuator fault codes.

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