To start the project, the original heater plenum case is removed following the service manual info. While the area is clear, the vent door should be checked for proper operation. The vent door uses a foam-rubber seal around its circumference to seal external air from entering the passenger compartment. A leaking seal will dilute the cold A/C and cause condensation. Now is the time to do it as it's impossible to service once the A/C system is in place.