Chances are about 95% that you have a very common problem on 850s: a broken recirc door linkage arm. If your recirc system is working correctly, you should hear a noticeable increase in fan noise and air flow when you engage recirc vs. fresh air (this is because the recirc path has less flow restriction). If not, the plastic door linkage arm is probably broken. If you have some mechanical abilities, you can replace it yourself, otherwise your dealer/mechanic will know exactly what to do because he's done it hundreds of times.

Gerald C