Abstract: A modular heating, ventilation and air conditioning system including a rectangular sleeve that can be secured through an exterior wall of a building for moving air between an exterior of the building and the interior of the building, an electrical outlet fitted with an electrical outlet adapter pan that connects the outlet within the sleeve, a through-wall air conditioning unit fitted with an air conditioning adapter collar that connects the air conditioning unit within the sleeve, a heater unit fitted with a heater unit adapter pan that connects the heater unit within the sleeve and an electrical system control module including a thermostat and control pad assembly, a first switch and a second switch that selectively activates the sockets of the outlet.