GM Service Manual Online
For 1990-2009 cars only

The most likely cause of excessive heat from the heater system is an improperly indexed temperature control cable. Other related causes include the following conditions:

    • A slipping self-adjusting clip at the temperature control cable end
    • A loose control cable sheath retainer or bracket at the bottom of the heater assembly
    • A binding or obstructed temperature air valve

A hot air leak from the engine compartment to the blower inlet is also a remote possibility.