Heater Core: Description and Operation

The temperature control in the control is linked to the temperature valve by a flexible control cable. When the temperature control is rotated fully counterclockwise to the full COLD position, the temperature valve is held snugly against the air entrance to the heater core. This causes all of the airflow from the evaporator to bypass the heater core and there is no heat transfer.

As the temperature control is moved clockwise away from the full COLD position, the temperature valve begins to direct some air to the heater core to allow some air to flow through it. The farther the temperature control is rotated clockwise, the more the temperature valve directs air through the heater core. Heating a greater proportion of the total airflow in this manner results in a warmer discharge of air because the heated and unheated air flows join and are mixed together thoroughly beyond the heater core.

When the temperature lever is rotated fully clockwise to the full HOT position, the temperature valve blocks off the passage that allows air to bypass the heater core and causes all of the airflow to pass through the heater core.