98 Dodge Caravan problem with passenger side heat

My 98 dodge caravan 3.3 liter v6 at, dual ac has a driver and passenger slide control for the ac and heat when the heater is on it works fine for the drivers side but when you put on the passenger side it blows out cold the ac comes out cold on that side any suggestions or things I could look at first thanks john the fire guy the vehicle has 133000 miles and transmisions rebuilt but runs fine.