Strange experience last night. outside temperature around 60F. A/C was on, temperature set at around 72, front seats have cold air coming out but rear seats' vent had warm/hot air coming out, including the vent from the door...

What is the problem?

Today around noon I started the car, turned on A/C same thing happened: warm air came out from rear seats' vent until I lower the A/C temperature to 69 then cool air started to come out.