Abstract: An air conditioning apparatus, including an electric motor driven blower for circulating air through a cabinet, also includes one or more electric heating elements and a system controller operable to control energization of the heating elements and the blower motor at predetermined operating conditions by way of suitable relay or control elements. The system includes a heating interlock relay to prevent energization of the one or more heating elements if the blower motor is inoperable, operating at other than a predetermined range of speeds or the system controller detects a malfunctioning heating element control relay or the like.