Differing temperatures through air vents
 

I have an issue with my 2008 Mazda 2. After finally getting the air con working having replaced numerous parts, I have now discovered that, when using it, cold air blows through vents on the drivers' side but the passenger side remains warm. It's the same whichever direction is used, floor, dashboard vents or windscreen. The vent system has been checked and all flaps operate correctly. Has anybody experienced this before or better still does anyone know how to resolve it please