I am having an AC problem. Cooling is not working right. Temperature is changing coming out of the vents. Some time warm and sometimes cool. Driver side ac vents seem to have colder air while the passenger side is blowing warm. Seems like a mixing problem between ac & heat. Also some times the AC seems to work and other times it does not. AC Freon charge was checked and is OK. Is there a temperature sensor somewhere that controls heat & cool? If so where would I find it? If not does anyone have an idea as to what I should look for?

Thank you for any help.