The blower motor is a new AC delco one, seemed fine with no issue with the wheel attached.

The air ducts are clean, I used my endoscope camera to poke around in the vent openings.

The heater core and evap fins are completely un-obstructed. Actually really clean in there.

If I select Defrost, if I recall noting comes out of the floor vents.

I need to measure the vacuum I think. The actuator near the driver foot is a new AC delco unit.

The actuator behind the glove box doesn't move at all, and I can't find my old videos that showed if it ever worked or not. When I had it out I pushed the arm in and placed my finger over the vacuum hole and it held position without issue.

 

Yeah, I'm pretty much checking every vacuum line.

4x4 works flawlessly, and I just did the transfer case fluid and there wasn't any transmission fluid mixed in from what I can tell. I opened the fill plug first and only a tiny bit came out. (my garage has a slight grade to it for water drain off.)

 

Can someone tell me where to look for the source line that feeds the driver fender actuator? The hose going into it was always secure and it has no cracks in it.

Really seems my issue is vacuum related.

In the driver foot well where the vacuum line comes in there's an elbow style fitting that I think has a spring in it which then leads to the vacuum junction (not sure what it's called)

This fitting had some black electrical tape on it - almost as if the previous owner was trying to fix this issue.

Anyways - any help is appreciated.

 

Did you ever figure out the culprit ? This is my first winter with the Blazer and I have similar problems and no 4x4 engagement.I got this about when you posted ! I am in the process of replacing all the vacume lines,after having replaced the Transfer case switch several months ago,and I thought I fixed the 4x4 prob.,but I haven't found the cause for my malfunction yet either. I am also convinced it is HVAC related since I cannot direct flow from the dash to the lower heat outlet. I think I may have fluid contamination in the lines etc. from an overfilled system 6/15. Those lines are difficult to trace !

 

I had same issue. I removed the motor relay, [under hood] Using air hose blower, [modified] blew out lots of crud. Kinda like blowing out air filter. volume increase