Actually with ozone machines in cars it’s the opposite. We’ve found at work that the very best combination is to put the ozone machine on the center console on a towel (that way the feet don’t put an indentation on the arm rest), turn the air conditioning ON, put the fan on HIGH, and turn recirculate ON. That has been the most effective. It runs the ozone through all the vents and the blower motor, which is hard to get to with the bombs. I’ve done this method a bunch of times in customers cars and it’s worked flawlessly. I did it in my own used beater I bought years ago where it was so heavily smoked in that there was a film on the window. Ran the machine in it for 6 hours or so and never even had a hint of smoke, even on a hot humid day where the car was sitting in the sun all day.