PT Cruiser - unusual odor

There is an unpleasant odor whenever the AC or heat is turned on for the first time. It usually goes away after a few mintues. Does anyone know of a filter or anything within the ventilation system that could cause this? Thanks!

make sure your drain on the firewall is not plugged up, or hose collapsed. when your car is warm turn your heater on full blast and unplug your airconditioner fuse or relay. run it for 10 minutes and it should dry it out. if that doesn't work you can buy some spray to spray into the duct work by the windshield wiper motor. if the dealer does it can be expensive. toivo