When I turn my ac or heat on is smells and has a sort of hissing sound

Hello, Dave here, contributing to RepairPal and providing expert advice since 2010. Your concern as described makes me wonder about whether the plenum and evaporator box is draining water as needed. This water is condensation and evaporated from the vehicle has the air conditioning system dehumidifies the interior. If it is clogged even somewhat, standing water may create an odor and could cause a noise. My thoughts are only a guess. But it's consistent with your smell as well as the sound. You could also have some other kind of contamination. Perhaps pull out the cabin air filter and inspect to see if you see anything. Seek help at a shop near you -- https://repairpal.com/auto-repair-near-me Click the link or call us at 877-913-1554. We'll gladly find you a certified RepairPal shop in your area.