Last year I noticed that my A/C was not as cold as it should be, so this year I took it in to get looked at. The repair shop said they evacuated the system and refilled it and it was blowing cold. After picking up the truck, I ran the A/C and it was warm air. That was a week ago. I haven't had a chance to call the shop yet, but today I found out that the passenger zone was blowing cold and the driver zone was blowing warm. Both temp dials were on Lo. What controls the temperature to each side so I can replace it?