A universal control system is provided for a room air conditioner or heat pump that has a number of sensor inputs. An electronic control system with a microcontroller and microcomputer are used to provide a large number of operations that can be performed by (1) manufacturer, (2) end users and (3) maintenance personnel. The manufacturer can load different versions of a software program to match the unit. The end user can program in a large number of different conditions or schedules the end user finds desirable, plus the end user is advised of maintenance requirements or faults. The maintenance personnel may perform diagnostics, determine fault history, upload improved or replacement software, as well as the numerous maintenance functions normally performed by maintenance personnel.