oder from ducts

1998 explorer i have an oder that comes from my vents only at a certain temp. 45 - 50 degs. almost like a mildew smell but i don't think it is, can anyone tell me what this is. thanks

It is mildew and odors caused by bacteria. During warm weather AC use, condenstation is building up in your air duct system. The moisture from this condensation mixes with dust and other impurities and provides the perfect environment for mildew and bacteria growth. Here is an effective remedy. Ouside and below your wiper blades is a perforated panel. With the engine running and vent fan blowing, spray about 1/2 can of Lysol down into the perforated openings on both the drivers and passengers sides. You will notice an immediate loss of odor and the residual Lysol in the ducts will kill off the rest of the odor causing mildew and bacteria growth. You should do this at least once per year or more if you are in a humid climate.