Temperature Control Knob

When the temperature control knob is in the "COLD" position, the air mix door closes to block the flow air to the heater core.

When the temperature control knob is in the "HOT" position, the air mix door opens to allow air to pass through the heater core and heat the passenger compartment.

Placing the knob in a intermediate position will cause a lesser or greater amount air to reach the heater core. In this mode the passenger compartment temperature can be regulated.