I'm trying to help diagnose the possibility of a slight evaporator leak. After sitting, the car in question (134a AC system) has a slight odor at startup. When running, there is nothing observable. It strikes me as the smell when a gauge set pops and some refrigerant and oil comes out. But it's not clear to me if odors of a 134a system are from the 134a itself, or if from the Poe/pag oil. I've obviously never huffed the stuff, and I don't vent it to the atmosphere. So does 134a smell or the oil?