Would anyone have an idea why my 2004 dodge ram 2500 only blows cold on the driver side? Thanks for your help.

There's a service bulletin out on this for the minivan. Take a look and see if this might apply to your Ram. If not, I would suspect a bad blend door actuator on the passenger side.

Passenger side heat/cool not responding to control (http://www.ricksfreeautorepairadvice.com/diagnostics/by-symptom/caravan-voyager-tc-2001%E2%80%94no-heat-on-passenger-side)

It has to do with the vent door located in your dash, it is made of plastic and is starting to break. If you have a master radiator shop near you they can fix this for you. If not you'll have to go to the dealer and just open your wallet. I have two rams , a 2002, 195000 miles and 2003 98000 miles both have had this problem and I got one fixed at the dealer (stupid) and the other fixed at master radiator. I will take my trucks there for this from now on. (every 3 years you may have to have this done) Love my Rams even with this little problem. :-))