Either a leaking vacuum line or a leaking evaporator.
The doorpanel is rather easy to remove.
Take out the plastic trim behind the door handle and remove the Philips screw behind it.
Remove the Philips screw in the plastic trim around the door lock.
Remove the Philips screw in the underside of the armrest (small hole visible from underneath).
Remove the Philips screw in the underside of the speaker grating and remove grating and speaker.
The underside and left/right side of the door panel are clamped to the door with plastic plugs; pull these gently out (straight forward). The top of the door panel is held by steel clamps along the window and needs to be pulled vertically upwards.
Disconnect the window switch from behind when the door panel is loose.
with a minor 600+k