There is a flap behind the glovebox that controls outside air circulation
into the car.
This flap is partly controlled by a spring which may have broken.
This would interfere with control of outside air circulating into the car
and may be the cause of "FogFogFog!"
While you are looking in there you ought to clean out the leaves, hair, any
dead animals, and other trash that probably have accumulated.
If you find the loop on the end of the spring has broken off you may be able
to reuse it, saving a trip in search of a new one.
Try bending a new loop with a pair of needle nose pliers.
I had the same fog problem and accidentally discovered it while cleaning out
the leaves, hair, etc. :-)