Heater blows cold air on 1992 GMC Yukon

Is there a heater water control valve and how do I replace/check it? Where is it?

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1 answer
First of all, make sure the coolant level is OK, and the engine is reaching normal operating temperature.

Your vehicle has a temperature blend door, and it is activated by a little electric motor called an actuator. Check out autozone.com for instructions!