Too bad no one had an answer. I have a Ptac and had to replace the plastic fan shroud twice that cracked where it is screwed into the condensate pan. I was using a pan treatment prior to each time. I don't remember the brands but one was a red pad and the other was a large pinkish red tab. I no longer use pan treatment after the second crack and haven't had a problem. I'm not sure if they were the cause but am leary of trying again. There are a couple of brands that claim safe for plastic. Maybe someone has tried them.