In cold weather if the temperature setting for driver and passenger side are the same (say 72 degrees) will the air be colder coming out of the passenger side vents if there is not a person in the front passenger seat?

 

Nope whatever you set the temp too that is what it will produce, no matter if it is in "Single Mode" or "Dual Mode". Now if you are in "Dual Mode" with different temp settings (your side 72 degrees & passenger side 75 degrees) your side will blow colder than the passenger side due to the lower setting.