Sometime back in the alt.autos.volvo group one of the regulars posted his
solution to the common problem of musty odor in A/Cs. The first step was to
ensure the drain hose was clear (it normally drains the evaporator housing
to someplace just in front of the passenger), then to turn the A/C on full
cold and to spray a mixture into the cabin air intake. I don't recall the
exact mixture, but the main ingredient was rubbing alcohol and I think it
included Lysol. The spray would condense on the evaporator and kill mold on
the surface, then run down into the drain pan and the drain hose.

Mike

Once the drain tubes are clear, this is the remedy one of the regulars in
the alt.autos.volvo group just reposted:

**************************************************
                Non-toxic A/C System Cleaner

  Mold, mildew and fungus growth in automotive A/C systems is a
common problem, especially when the air intake control is
regularly set to "recirculate" or "Max A/C". There are commercial
cleaners available that can control the problem, but I have yet to
locate one that isn't both moderately toxic and strong-smelling.
Since I'm somewhat sensitive to noxious odors and to chemicals
like ammonia, I have developed an easy to mix, non-toxic
alternative that, for me at least, works as well as or better than the
commercial products. In the interest of a less-toxic environment
and as a public service, I am posting it.

                     Materials Needed:

Clean adjustable spray bottle, preferably 24oz or smaller.

Cheap vodka

Apple cider vinegar

  It is probably possible to use white wine vinegar, but I haven't
tried it. Feel free to experiment, at your own risk. Mix the two
ingredients in the bottle: three or four parts vodka to one part cider
vinegar.

                       Application:

  With the recirculate control set to "fresh", the ventilation fan on
medium, all windows open ,and the engine and A/C running, spray
generous amounts of the mixture into all of the outside air intakes.
These intakes are usually located at the base of the windshield. If the
system is already seriously moldy, wait a minute, set the air intake
control to "recirculate" or "Max A/C", and spray the mixture into the
air recirculate intake, usually located above the front passenger
footwell, or sometimes behind the glovebox. Let the A/C and fan
run for another minute or two, then switch off first the A/C, then
the engine. The car will smell strongly of vinegar for an hour or
two, but I find this to be both far preferable to the smell of the
commercial cleaners and shorter-lived. Leave the windows open a
little when finished, if possible.
  Like commercial cleaners, one application may not be enough,
so I suggest weekly applications until the problem is gone, then
preventative treatment once a month during warm weather.

                        Precautions:

   This formula is non-toxic, but not completely harmless. Use
common sense when applying it. That means not getting the spray
in eyes, nose or open wounds, and not applying it with people or
animals in the vehicle. Depending on the proportions (and again
like some commercial products) the mixture may be flammable, so
don't apply it while smoking or near any combustion source.

   As with the commercial cleaners, remove any residue from painted
and/or plastic surfaces after application, as it may harm the finish.

  Finally, don't drive the vehicle until the vapor has dissipated; not
only is there a slight potential for intoxication, there is also the
possibility that this cleaner can produce a false positive on a police
breath alcohol analyzer.

              Copyright 2001, by Michael Cerkowski.
              Distribute freely, but do not modify.