The Jackson Systems TK-400 is a universal twinning/paralleling kit designed to allow a single thermostat to control multiple HVAC units. It was engineered to incorporate solid-state, diode relay logic with all components and wiring terminals mounted on a single, compact, printed circuit board. The PC board is mounted on a Snap Track base to facilitate ease of installation. Only standard 18 gauge thermostat wire is required and the HVAC units and thermostat can be located up to 300 feet from the panel. A separate 24 volt, 40VA transformer provides power for the panel and controlling thermostat. When used with fossil fuel furnaces sharing a common supply duct, back draft dampers are required and the controlling thermostat must be equipment compatible. The TK-400 can be applied where multiple HVAC units are used to condition large spaces such as church sanctuaries, fellowship halls, recreation areas, warehouses and manufacturing facilities as well as other applications where large packaged RTUs can not be applied due to roof pitch and load restrictions. The TK-400 can be applied to HVAC units sharing common or separate supply and return ducts. The TK-400 saves hours of installation time by incorporating dedicated terminals for all system wiring. LEDs provide visual confirmation of equipment mode of operation, fan, reversing valve (heat pump only) and staging status which simplifies servicing of the system. The panel does not require any system setup. Status LEDs provide visual confirmation of system functions that simplifies service and diagnostics.