Little Electric Motor/Fan Behind Dash
The volume of air being moved by the little motor-fan assembly is very small. As I recall, that unit is 2 - 3 inches in size. The small amount of air is expelled into the area above the passenger's feet. Mine runs all the time, ACC or no ACC.
I too had concerns that this little motor had quit. My 126 has air bags, so I was reluctant to probe around the area of the passenger's air bag to find this motor/fan. Curiosity got the better of me for a collection of reasons.
From memory, working from the passenger's footwell, to access the little fan (which is located next to the main ACC blower plenum) remove the 3 ? vertical screws that hold the knee bolster/change tray in place. Then pop out the plastic face plate/escutcheon in the passenger's change tray to remove some remaining screws (in this 126 I have learned that escutcheons should generally be lifted out from their right side, pivoting at their left side). The air bag wasn't an issue since it is mounted well above this area.
It's been awhile, but I believe the visible little motor is then accessible. If not, there are 3 bolts that hold the passenger side metal ACC plenum in place. ( The 3rd bolt is cleverly accessed with an extension on a socket wrench) Removing that plenum exposes the little motor in question.
In retrospect, to check the viability of that little motor is easier done by using the often mentioned tissue paper test. Since the suction is so weak, I found that it was a more certain test if the overhead grill and light assembly were lifted out, the plastic tubing to the temperature probe removed, and the tissue paper placed over the open plastic tube. If the paper sticks, the motor and fan are functioning. I am guessing, but I don't think that its necessary for this whole assembly to be so powerful that it will draw inches of vacuum.