Anyone else park their car outside? If so, does your car's rear defroster able to dissipate the morning dew/fogging?

Took the car in to stealership to have them check out the rear defroster as when I turn it on, the morning dew/fogging is not dissipating. After running continuity test, they told me all is fine and the rear defroster is just that, defrosting only. (ie. ice/snow).

Brian