I've had 2 850's & both of them had this same problem. Try this to help diagnose the problem...

Turn the key to on, but don's start the car. You want the heater controls active, but the car quiet. Toggle the recirc switch & listen carefully near the glove box. You should hear the motor activate each time the swith is flipped. If so, the motor is working.

The most common cause is that the plastic level arm breaks.

You can easily replace it yourself. It is accessible by pulling out the glove box.

With the glove box out of the way, you can look in while toggling the switch & see the mechanism work. It sould be obvious what part is broken.

Mike