Heating and cooling acting weird. Will blow air through chosen vent, sometimes. Then just stop! Fan still blowing, just not coming out anywhere. I believe there is no filter on these models.

 

If it reverts to defrost, it's probably a vacuum leak somewhere.

 

Well the air must escape somewhere. Check if it's coming out of the windshield and foot vents. The vacuum, as stanvan said, is your most probable problem. The vacuum reservoir is a plastic sphere mounted under the battery tray. Inspect the hoses and tees coming to it.
There is no air filter.

 

Most cars are designed to revert to defrost when vacuum is lost. It's probably considered the most important setting.

 

Thats the problem. Its not coming out anywhere. Doesn't defrost either, a major issue with the cold weather now. Today, on the way home, I had it set on hot to cabin, and for 15 miles, nothing. Suddenly, started blowing hot out the vents and stayed on all the way home.