The "Air Mix" system enables fresh air to be supplied through the center ventilation outlets while heated air is obtained from the other outlets. Unless you are using the system's heat its most efficient to leave the Air Mix closed. Do your "Rec" and "AC OFF" LED lights flash for 20 seconds when you first start up the car? You can check for any stored DTC codes related to the A/C system using the "B-box" of the diagnostic terminal boxes behind the right-side headlight. Put the contact pin (found in the "A-box) over into the position One hole in the "B-box" and turn on the ignition. You will see a series of three flashes in the "A-box" LED (kind of like Morse Code). It will be something like 1-1-1 hopefully but not likely. Count the flashes in each series and write them down, then come back here and post the results. I'll tell you what the codes mean and that will help narrow down your search for the cause. It kinda sounds like they may have broken an actuator arm off one of the damper motors or something when they worked on the blower motor (if they actually did the work they would know the problem). Do you have a repair shop that is reliable in your area? Ask around and see who has a good reputation for A/C system repairs with Volvos in your area. It could be a broken actuator arm or that the damper motor limits (vent dampers) need to be reset after work has been done improperly. Let me know what you find out. Good luck ....... Mike