The "fumes" are more than likely antifreeze from a leaky heater core.
It is called condensation.
replace? why not fix it?
yup, sign of a bad heater core
Nope, that would be steam.
Generally, with that smell- the heater core has gone bad.
The musty smell coming from your AC vents could be caused by mold or mildew growth in the system. This can occur due to moisture buildup in the ducts or filters. Regular cleaning and maintenance of your AC system can help prevent this issue.
assuming this is Home AC question - speed up the AC fan speed
is it because of a lack of vacuum pressure?
Perhaps a dead mouse.
There may be something blocking the deflectors from sending air up there.
Those "fumes" are more than likely coolant steam coming from a leaky heater core. Replacing the heater core is your best option.
A pipe that vents fumes