i have a 2006 gmc envoy denali,all of a sudden no heat control or vents ,i put a new fan blower in but it makes a clicking noise when i turn it to defrost…
It sounds like your blend door actuator is bad. the plastic gears get stripped with age.
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Agree with @weekend-warrior … common failure for GM vehicles. Usually not too expensive to replace them.
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No heat would be the blend door actuator. For example, the output air location can be changed but the temperature can’t be changed.
Clicking when you change the selected output (floor/vents/defrost) is probably the mode door actuator. The air will get hot or cold depending on selection but the place where the air comes out cannot be changed.
It’s hard to tell from your description but sounds like you have both problems…