My 2008 outback has similar problem. The AC works for 45 minutes then the vents stop flowing air. If I stop for five minutes or switch the AC off for five minutes the AC and vents work again. I think the core is freezing over and blocking the vents. When you stop the AC the ice melts and opens the vents. There must be a sensor that switches off the AC so that the core defrosts. I had a dehumidifier that had the same problem. I am going to the dealer to get it fixed on warranty on Monday. Does anyone have a similar problem and did the dealer fix it?
It is typical for the core to freeze if the R-134a refrigerant is low. This will probably be the diagnosis. Let them fix it under warranty, but if it is low, don’t let them just add R-134a and send you home. Have them find the leak while it is still under warranty.