Q:

toyota corolla 2001 air duct smell

My 2001 Toyota Corolla recently started smelling very foul whenever the air system was turned on.  According to the research I've done online, there is no cabin air filter to change.  The glove box seems unable to be removed, so I can't see behind that very well.
The dealership where I bought the car is not in the town (or even the state) where I live. 
The research I've already done claims there is no cabin air filter for a 2001 Toyota Corolla, but I can't figure out why it smells so foul.
Can anyone give me advice on what action I should take?  Also, if you suggest that I take it into some sort of shop, how much should this cost?  At the Toyota dealership here in town, it costs $87 for a diagnostic. 
Thanks.
(Note:  The car smells poor because it's somewhat unclean, but there is a very distinct and very strong bad smell from the vents whenever the air is turned on.  The smell comes from both the A/C and heat.)

A:

It sounds like you have mildew in the ventilation system.  We've discussed similar situations a few times before: here and here.  You probably want to check those questions and decide whether what they describe applies to you.
Apparently, you are correct: the Corolla did not get a cabin filter until 2002.  That's annoying but isn't a show-stopper.
As a first step, I would try running the heater at maximum with the system set to air conditioning.  That sounds crazy but the goal is to eliminate moisture that is likely trapped in the system.
Next, clean the car out - there's a good chance that a dirty car has mildew in the floor mats and such.  Get those out in the sun and wash them off.  Vacuum out the interior if possible.
If you don't see improvement from both of those, proceed as seems best.  Here's what I would do next:
Go looking for places where you can rig up a filter to substitute for the lack of another.  I wouldn't think of this as a permanent fixture - just something to reduce the spore count.
For example, our local big hardware store sells HEPA furnace filters for fairly cheap.  Those are easily cut to whatever size seems appropriate.  You can affix a square of filter material to the outside of the air conditioning recirculation intake using duct tape, if nothing else.  
Clearly, that would be a bit ghetto.  Still, you would be pulling the air through a filter and that will reduce the spore count over time.
Hopefully, you'll see sufficient progress that you won't have to open up the whole vent system.

