Why would I feel cool air from my defroster, which is in the hot position, only when I turn?

has some work been done on your cooling system...what is happening is the heater core is air-bound and just hasn't got the flow to push the air bubbles along, some manufacturers have a little thumb screw on the corner of the highest place on the heater core, but I've found it's best to put some gloves on when it's up and running at operating temperature and disconnect the return line for a moment to let the air out and re-connect, as I've stated this should be done with good gloves on because it's BOILING hot!...or take it to your shop and ask them to "belch the heatercore", probably for not twenty bucks will take care of you.

the thermostat has to be functioning normally, that is to say it stays closed until the engine gets up to 195, then opens up, releasing the coolant into your heater core (if the selector is set to hot)-....so you may need a thermostat-

I got the car as a used vehicle this past summer and this was the first winter for me with this car, so as far as past work, not sure. Carfax only showed regular maint. done. It has 73000 miles and I wonder if doing a flush would take care of it as well?

If it's not givin' you trouble, then drive on! driver.

Make sure your tem gage is showing engine hot before turning heat to on !