So my AC is blowing ice cold down here in Sydney Australia but for some reason when I have it on external face mode the windscreen fogs up, seems it is blowing air there while it’s on face mode. Does anyone know what the issue is? Thanks

 

Fogging up is an indication of a leaky heater core.

 

I agree with Cruiser. However I would like one more piece of information. Does it smell like engine coolant inside or is it nice clean fog?

 

Its just clean, its only when i have the air blowing, i am thinking maybe it could be a flap issue or something but i dont seem to have any other issues, have not tried the heater in a while since its summer over here but the AC was not working for quite a few years, i just fixed the AC system recently.

 

My first inclination was heater core.

However, could possibly be your AC condensate drain is plugged and filling up with water. Insects sometimes get in and build a mud-nest. Or a piece of foam could have broken off around the core and plugged it from the inside. Check that it's draining properly and remove any blockages. If the condensate is flowing it could be the heater core. If it is, eventually it'll get a lot worse and you'll know for sure.

 

Condensate drain, yes. But I think you have only partial vacuum to operate the mechanism. It defaults to defrost and I don't think it is changing completely over

 

How can i verify there is an issue with the vacuum?

 

You can hook up a vacuum gauge to your lines. But the most common cause is a crack in the vacuum reservoir located behind the front bumper on the passenger side