'91 HVAC control door

1991 model ... is the big flap thing under the passenger dash with the vacuum deal the directional control? If that's the right thing, does anybody know what the vacuum pressure on that orange hose is supposed to be?

The vacuum on the line is very low (less than 5 hg) and the air outlets change as I accelerate which suggests that sufficient vacuum is not being maintained. Engine vacuum tests acceptable--about 18 hg at idle, which drops to 10 hg on extended acceleration, and rises to 25 hg on coast--and it all tests the same with or without canister and also with or without climate control vacuum line. I would think some loss of outlet control is expected on extended acceleration (the canister is too small to hold vacuum stead for very long), but it really shifts dramatically.

The flap under the passenger dash is the recirc door. It opens when the climate controls are turned to OFF or MAX, but is closed otherwise. 3 hg appears to be enought for it to operate.

Where is the HVAC control door?

The HVAC control door is in the climate control unit itself. There is a little miniature vacuum harness at the back of the control unit that is used to manipulate the individual air outlet flaps.



The input line is the black hose on the left just below the white loop. Testing with a vacuum gauge shows that it maintains pretty even 10 hg inches although it does drop a little bit. I applied some silicon dielectric grease and then picked out the tubes so that they wouldn't get clogged, firmly reseated the harness. It works much better now, although there is still some minor drift under extended acceleration.

This is the first day A/C has worked in at least three years