Written A few things:Your air conditioning system does not have CFCs, they were banned decades ago.Even if your air conditioning did contain CFCs, running the air conditioning would not release any CFCs to the atmosphere. It is a working fluid inside the device, if it were leaking your air conditioning would soon cease functioning.The rate of cooling depends on a lot of things that can't be answered. Some air conditioning systems will output the lowest temperature reachable by the air conditioning system (which depends on outside air temperature), and do so until the room reaches setpoint; in this case, it makes no difference if you set it to 24°C or 4°C. Other systems will adapt the supply air temperature based on the selected temperature (commercial applications), in which case it does make a big difference what your selected temperature is.Written Many thermostats are simply on/off switches.  If it's hotter than the set point, then the AC is ON.  If it's colder, then it's OFF.