The 123's have a mechanical evaporator temperatur control that is set to cycle the compressor off at about 48 degrees evaporator temperature. This is not very cool to most of us since most other cars use about 38 degrees for this cutout. Additionally there is a cacuum controlled solenoid that closes a door limiting outside air into the system. If this is bad then the system continues to try to cool down outside air versus recirculated air. Both of these can be modified or repaired for better performance, especially if you are in someplace like Texas, NM, AZ, OK, etc where the heat is oppressive.