HVAC Blend Door Actuator. HVAC Actuator. 1999 GMC Sierra 1500 Engine: 4.3L V6; Actuator; Temp Valve | Bottom;. 1999 GMC Sierra 1500 Engine: 4.8L V8; Actuator; Temp Valve | Bottom;. 1999 GMC Sierra 1500 Engine: 5.3L V8; Actuator; Temp Valve | Bottom;.