A heating, ventilation and air conditioning system for a vehicle is constructed from two modules, one for the engine compartment and a second for the passenger compartment. The engine compartment module has a base formed for positioning on at least two locations on a dash panel, a outside air inlet, a secondary air inlet for communication with the passenger compartment, an air outlet and defining a air transport conduit connecting the outside air inlet or the secondary air inlet with the air outlet. Downstream from the engine compartment is a passenger compartment module having a slide slot for a heater core, an inlet for communication with the air outlet from the engine compartment module, an air manifold, a panel exhaust from the air manifold, a defrost exhaust from the air manifold, a compartment door providing access to the slide in friction slot, and an air channel from the inlet to the air manifold. The heater core is positioned in the slide in slot.