2003 Jeep Grand Cherokee blows cold air one side?

You might want to check on the side right beside the vent. There is a switch that goes up and down with a solid square on top and an open square on the bottom. This controls whether or not your vent is open or closed. Just try sliding the control to the open square and that should open up your vent. If that doesn't work then something could be blocking your vent. Such as a clog.