I have a 2005 Ram 2500 with the diesel engine. My a/c blows cold on the drivers side but not on the passenger side. I have cheked the levels and they read fine. When I switch to the floor or defrost, it blows cold out of those vents. It is frustrating and I need some help figuring it out.

 

check your manual for dual side blend doors. you'll find one of the doors is open all the way allowing outside air in all the way. there are dual dampers in the duct that allow for air to flow in various amounts from outside and mix with conditioned air thus regulating the output temperature of the outlet air temps. (some have a single door when there is only one zone). if you find the door is open then you must do the step by step troubleshooting to find out the cause. it could be the actuator motor (servo), or control on the dash. most likely though its the servo or it's wiring as the other side is working. not sure how they're wired as mine is single zone. on mine the axis point on the flap/damper broke (it's plastic) and the damper just sat there and jumped up and down making a banging sound until I removed it for replacement. the mixing of air from outside is how your system can have dual zones with only one compressor/evaporator, etc.