Never. The car is only 4 years old, though with 60K miles and of course recently out of my extended warrenty.
It seems to work fine. Cooling in the summer and drying/defrosting in the winter.
I'll have to look into this some more. I keep forgetting to stick my noise under the hood when I get home. Maybe it's because Shelby is right there at my door waiting for me to step out when I get home!
)