I had a new HVAC system installed 3 years ago. Going back between heat and AC this time of year. When I turn on the AC, it get this 'Dirty Sock" smell. I've used the spray "Dirty Sox", as the HVAC people use. It works. Just wondering if there was a more permanant solution? It's a new system, should not do this. It's a heat pump, Trane Seer 16 (Lxi I think). We replaced everything both outside and inside, except the duct work.