Pontiac Repair: bad smell air vents 2000 grand am, fuse box, buick regal

Question
when I turn on AC, bad musty smell comes out at first, then goes away as it cools down.  How do I fix this?  I read theirs no filter for this year but could install buick regal filter?  what do you think?

Answer
Hi Bob:
this is a common problem with all cars particularly if you live in a area with high humidity. Gm has a product that is a coial coating spray. you have to drill a small hole in the bottom of the heater box and it has a long spary nozzle you put on the can to reach up into the heater case. it will kill off the bactria/mold causing the odor. you drill the hole in the box between the blower motor and the evap core. run the car with the heater on and NO ac for 15 minutes to dry out the box. then turn the a/c on and pull the relay out for the compressor in the fuse box turn the temp dial all the way down to cold and then use the coating. with the fan on low speed and pull the spray nozzel back and forth in the hole to try top get an equal amount of coating on the core. There is one more step to this if you choose it's called an after blow module It's VERY expensive but what it does is in the right teampature setting it will turn the blower motor on after the car has been running to dry out the heater box and eliminate the chance for the mold to drow again. Oh your right no filter for this year car and no a regal filter will not work on this. Good luck :)