What causes a film on the windshield, also a smell when heater is on? on 1997 Mercury Cougar

It casues my eyes to burn and my heart to race.

Asked by for the 1997 Mercury Cougar
our heater core is leaking antifreeze into the heater air box and the film on the windshield is engine coolant if the film is easly streaked as u wipe it then deffenently that will cause your problem