Why does AC on passenger side to not blow cold while on driver side it does? on 2000 Jaguar S-Type

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Has individual climate control. With temp set at any temp (equal on driver side and passenger side) the passenger side AC blows air but it is not cold. Driver's side air does blow cold.
(1) Answer
It sounds like your hvac heater control valve solenoid. This opens and closes the valve that allows the radiator to pass hot antifreeze through hvac system for heat. There should be two solenoids because dual climate control and the one going to the passenger side is probably stuck open keeping the heat on that side. Not hard to replace just not sure if both solenoids are one piece or if you can replace them individually.