Abstract: An improved modular air conditioning apparatus featuring selective panel enclosures, plug-in controls, orientation selection and servicing capability, the apparatus comprising an open box frame having three access sides which are each selectable for enclosure or component orientation. A blower and heat exchanger are disposed in an operating section of the frame, and these are removable through an access port provided by the removal of an intake grille disposed at one of the access sides. Riser pipes disposed in a vertical riser duct connect with other like units and supply hot or chilled water to the heat exchanger. A plug-in control assembly senses an external temperature and controls the operation of the blower which draws air through the heat exchanger and blows the air into a plenum section of the frame from which the air exits through an outlet grille.