I don’t have a side in this but both my ‘93 Ford Escort and my ‘01 Ford Crown Victoria would turn on the A/C compressor if you hit the Defrost button for the windshield.

Edit: Just searched it and I think you two are in a semantic misunderstanding.

The moist air freezes to the coils of the ac unit, which is than heated by heated air and drips out of the vehicle through a condensate drain.

How do you not understand that basics of an air conditioner? It doesn’t just cool, it conditions the air.

Wouldn't it be more efficient to pass the cold dry air back over the hot side heat exchanger to increase its moisture caring capacity before blowing it at the glass?

You know like a dehumidifier?

Air conditioners make it cold inside the unit at a condensation surface, collecting the water from the humid air there.

But that's not how you defog a window, you heat the window until the air in contact with it can hold more water and so the water evaporates faster due to both water and air temperature. THEN this air can be pulled back into the AC to deposit it there with condensation.

Window / mirror defog doesn't work like regular dehumidification that way. Especially not in cars / bathrooms where you might be having a too high stream of humid air coming in, then you focus on one surface (and since the windshield don't tend to have heating wires, it uses the AC hot air)

This isn't just an American car thing, non American brands do this as well. That's because it's a good idea. The heater core has way more capacity than the AC, so the air coming out of the vent will still be warm. But running the AC is still a good thing, because it gets the moisture out of the air.

Without running the AC the humidity in the car shoots up and takes a while to clear, with the AC on the humidity stays controlled. This helps clear the windscreen sooner and helps with comfort in the car. It also prevents mold, which if you live in a cold but humid place, can be very annoying. It is very normal where I live to have the AC on in fall and winter, because otherwise the humidity inside the car is very uncomfortable and can easily cause mold all over the interior.

Is -20°C regular winter temps for Canadians? It's colder than that here in Minnesota

I guess cold is a relative term. I'm from Wisconsin- we can have 100% humidity at 65 degrees sooooo

Thanks, just didn't know how far we strayed, my first car had separate keys, apparently the new one can detect air quality and automatically close, new is also relative.

True, I mean just for heating using engine is cheaper.

I had kinda thought it was from my breath, but I never really looked into it. Could be all three?

The entire right side of the dashboard is missing, all the way down to the firewall, no thanks to the previous but now deceased meth tweaker owner.

There's no fixing everything on this truck, short of dumping enough money into buying 4 more scrap trucks for spare parts...

“Here” is an important word! I assume you are Canada based. I live where we rarely or ever get freezing temperatures, and only decently started having warm/hot summers. Why would defrosting or ac be mandatory in such climate?

Well I take it we're not in your state or country. Mississippi here, we no longer have vehicle inspections. And this is respected even in other states that do require vehicle inspections. They're like yeah fuckit, half the windshield is cracked, but it's from Mississippi, so nothing Louisiana can do.

Down here, we're half-professional rednecks that try our best to keep our own vehicles running. As long as it starts, runs, stops, shifts gears, steers, and has all the critical lights working, it's fine.

Hood, trunk, windshield, front grill, rear bumper, doors, heat, air conditioning, etc luxuries are all optional here. As long as it runs, stops, and steers is basically what all Mississippi cares about, plus lights at night. And other states have to observe our very lax vehicle requirements too.

I'm still working on some of the finer things, like it needs a horn, but generally speaking the truck runs pretty damn good to be 30 years old.

My 78 Chrysler was designed to use the AC in defrost mode even in a winter blizzard and was much more effective and drying the windshield because of it. Most heating/cooling system in cars were combined much earlier than that to take advantage of dehumidifying the air. It also has the benefit to run the compressor to keep lubrication and stop seals from drying out in the AC system that would otherwise not be used to months at a time.

There are some vehicles with separate heating and AC systems, (mainly cheap or aftermarket units) but the vast majority run together. (At least in North American cars.)

Uhhh my 96 civic had an air conditioner button, and it also turned on when you turned the defroster on.

You’re making shit up, it’s a simple interconnection, and the physics of air conditioning removing moisture has been known for a long time.

During winter snow constantly gets inside of a vehicle, so without an interconnected ac with defrost, the interior would always fog up. It just may not light up the button, but defrost turns the ac on.

My 2015 vehicle does it that way (a/c on for both), so it's not exactly a recent change in design philosophy...

No need to be an idiotic pedant. I said defrost, not front or rear, and posted an easy picture because I figured that anyone who had the capacity to read would understand what I was talking about. Clearly I was mistaken.

You've never had the ac on and see where the condensation blooms up from it?

Cities built around companies are also an exception, yes.