[17Hatch6MT]

vehicles defrosted windshields for years without A/C

I remember having to use rags to wipe fog off the inside of the windshield. Only after the car warmed up did the heat defrost work. And then you had uncomfortably hot air blowing on you, at least until the windshield heated up enough so you could turn the fan down.

I do think the heater-defrosters of the past were better than today's units, that don't have to be as efficient because the a/c dehumidification works so well. Maybe the problem with today's units (in heat only mode) is the a/c evaporator holds moisture that has to be 'burned off' before the windshield starts to defog.

That said, I would like the option to use hot air only & not run the compressor. Too bad we don't have that option any more, without doing 'silly' things like you're suggesting. My old Sentra had an unlabeled detent on the rotary knob that would defrost w/o AC. Unlabeled so it didn't confuse the 90% of people who are clueless I guess.