The service technician that I have consulted diagnosed the problem as dirty sock syndrome. My AC when operating emits a strong musty odor that lingers for a while after the AC cuts off. So I am pretty sure that it is an AC problem. I am not so sure of his solution, which is to apply a "biocide" to the evaporator coils to kill the mold, etc. I would like to be sure that this solution will work before I give him $300 to do this.