A/C vent kinda smells

[Probedude]

Had this same problem with our '01 PT Cruiser.
The vents would smell like cat piss after running the AC and then turning it
off.  Would linger for days.  Real pleasant. . . . NOT.

It is caused by mold and fungus grow in the evaporator.   On the PT, when
you remove the blower motor assy, you have a clear shot at the evaporator.
I bought a can of Ozium from pep boys (neutral smelling kind, large can) and
dumped the whole thing into the evaporator.  Been fine for the past 4 months
since I treated it.

The dealer sells stuff for $40 a can, 'glycolized' stuff, which Ozium also
uses.
Others have suggested using Lysol but I'd be afraid of using something that
would etch or corrode the evaporator.  They are usually made from extremely
thin walled alum tubing.

The dealer can and others online have tried just spraying into the air
intake vent on the outside of the car below the windshield.  If you can get
to the evaporator, this is a better way to go.

I have no experience with the foaming stuff.  Try the Ozium, it's under
$5.00 a can.  It is atomized extrememly well and takes a long time to dump a
can into the evaporator even though it is a smallish size can.

Dave