01 silverado 4x4

My heater is on even though the control calls for air . Is there a usually broken item for this, A rheostat or module and where is it located? Truck has 110,000 miles on it
TIA for your help
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Could be either the Blend door or the water valve.
Cheers
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On May 9, 10:05 pm, "Larry and a Cat named Dub" <hdyman58

My 2000 has had 2 blend door actuators so far.
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