I didn't find a thread for this topic, though I am new here. I believe my Heil unit (1997 model - but most major parts replaced recently - did I mention that it's a Heil?) has DSS due to a foul odor coming from the floor registers. Our recent weather has been cold then unseasonably warm, then cold again, and now sweltering, so the heat/air cycles have seen lots of use. Most recently, when temps got to the high 80s, turned on the air and received a stinky surprise. We have checked crawlspace to be sure there is no lurking animal, etc. A friend mentioned DSS and I have done some research, but was very confused by many comments, but few solutions. Anyone had experience with this issue? Thanks.