Why would the passenger side be cooler than driver side for air conditioning

Do you have automatic climate control? If so, you can adjust the temperature on each side individually therefore the passenger side temp. could be set at a lower setting. If you don't have the auto climate control, the air blowing into the cabin will be the exact same temp, but the drivers side air ducts could either be closed or have a partial blockage. Check the air gates on the vents to make sure they are open, or you can close them more on the passenger side to balance them out.

Because that's where the evaporator is located.