I had a Trane package unit installed last September. Right after I sometimes noticed this smell but never associated it with the a/c. But the past few months its been very strong, this is the first time a/c has been used 24/7. The last 3 days I left the unit off until noon and there was no smell but the smell come back after its turned on and gets stronger the longer it runs. The smell is like a freshly lit match or gunpowder. No smoke. Unit seems to be working normally. Does this sound familiar to any one? I'm going to call the company that did the install but would like to get some input first.