Hello & Welcome to JA,
Is your system manual or automatic temp control ?
Ok, this is computer controlled With actuators/electric & vacuum controls. The first thing I would do is to view the information from data & fault codes in the electronic control climate module. One will need access to a scan tool that will access the BCM (body control module). Make sure the vacuum to the to the vacuum solenoids is sufficient/ engine vacuum & holding. Here are a couple of pics . The control or the solenoid pack can be at fault IF there is good vacuum to this control.