Oh great and wise Blazer wizards...

I've only posted a couple times with questions, usually they're answered already.

2000 Blazer, automatic climate control

My blend door stays in the cold position. Pulling the RDO fuse to reset / calibrate the actuator results in the blend door moving all the way to hot (I think that's the hot side), then stopping at different points along the way back, only to stay on the cold side, where it remains no matter how the controls are set. Video here:


Heater core recently flushed both ways (core replaced a couple years ago), system flushed, new radiator, new thermostat, new coolant.

Just replaced blend door actuator yesterday with correct AC Delco part. Heard a not-so-reassuring clunk sound on first initialization though...

I'd love some advice on what to do next, as I'm out of ideas and I have searched like crazy!