Had the same problem. After years of deteriorating dashboard insulation blowing out of my air vents, this problem started. A friend/mechanic went into the evaporator w/ a scope and found that the coils were totally clogged w/ the insalation and debris. This was causing the coils to freeze up and the cold air to find the route of least resisitance. Hence, cold air to the drivers side and warmer, less air to the passenger side. A water hose to the coils for a complete rinsing took care of the problem. Place a plastic tarp on the passenger floor board to protect your carpet. Air blows cold through all vents and much harder now but be careful...this fix can get messy. Hope this info helps.

 

i hat being the one with bad news.
my truck was doing the same thing, it was my A/C EVAPORATOR, when my compressor let go i assume some of the crap got into tha evaporator clogging half of the EVAP. once it was replaced it works fine,,

 

OK... I’m at a complete loss as to how to remove the top dash on my 2005 3500. I’ve removed all visible screws and bolts and the dash will not come out. I’m afraid to yank on to hard. I’m removing it because the AC blows cool on the driver’s side but the passenger side is hot (in Phoenix). Sometime when I go around a corner the passenger side starts blowing cold so I’m pretty sure it’s the blend door. Any help?

 

I have this same issue. What a PIA. I think I will live with it.