Abstract: A bypass device to seasonally bypass an evaporator coil in a building's HVAC system to improve efficiency and reduce dust accumulation. The bypass device comprises one or more bypass diverters around an evaporator coil in an HVAC system, wherein bypass doors may be manipulated so as to close the air path through the evaporator coil and force air to flow through bypass diverters instead. The bypass doors are adjustable using control arms and may be maintained in either a flow-through or bypass position, so as to permit the air flow to travel through the evaporator coil, or bypass the coil, as the operator chooses. The control arms may alternatively be manipulated by a motor and connected to the thermostat so as to automatically select the appropriate position depending on the settings of the thermostat.