Let me guess, the drivers side is the one that is acting up? Either way, sounds like a broken temperature actuator. Pretty common on the dual climate systems.
Yes. Like right now with temp. turn up on both sides, the driver's side will get no heat at all, just cold air, pass. side has heat. AC on, the driver's side has ac, but not pass.
Is the is actuator easy to locate, where might it be.