This is one of those stupid facts that lives rent-free in my head. "If you want 'dry' hot air you need to dry it before sending it to the heater. The primary purpose of the A/C is to dry the air(this also happens to cool it), there is already an A/C unit in the ductwork, profit" But I decided to fact check myself and was not able to find much information. I did find one page that said this mainly occurs on the "defrost" setting, which makes sense as this is what is used when you don't want your windows to fog.