Unscrew the negative battery terminal, remove the heater control trim panel, and pry out both instrument lower trim panels. Take off the control cables from the heater unit parts, then take off the electrical wiring plugs and grounding wire. Unscrew all bolts that hold the A/C Switch in place. Do the opposite steps to install the heater unit, and fasten the ground wire properly. Push the levers forward on the heater cables while holding them in place, making sure the cables move through the whole operational range.