If the A/C, which I figured out how to properly operate by turning the knob juuuuuust so, is blowing out the main vents the engine runs great. If the engine is running not-great I can tell because it idles like poop and the A/C blows out the defroster. Pretty sure the blend door weirdness is a symptom of a large vacuum leak somewhere in the system, so I guess I’ll unhook the blend door vacuum lines and cap them off and see if the problem persists. On the plus side: *OH MY GOD THIS A/C IS AMAZING*. It is, in fact, so good that condensation pools under the dashboard and drips down on my feet when I go around corners. Which would explain the rusty foot wells.