Leaderboard

That gear drive actuator you replaced controls hot to cold blend. There is a vacuum switch behind the glove box that sends vacuum to separate vacuum doors to control what vent the air comes from. That black plastic vacuum line that powers the vacuum doors goes through the fire wall between the master cylinder and the strut tower. This is what the vacuum door controller looks like. https://www.rockauto.com/en/moreinfo.php?pk=14268801&cc=1021374&pt=7036&jsn=531

You should be able to get at both sides of the heater core...return is at the front of the engine, that long steel piping that follows along the right side frame rail that sweeps upwards to the coolant pump manifold, the inlet side is right beside the brake vacuum booster, a short hose that passes overtop of the master cyl reservoir slipping over the steel supply pipe from the bottom of the thermostat housing.