Overview
- Briefly opening doors or windows to expel trapped air measurably lowers the cabin air temperature and should be done before switching on the air conditioning.
- Cambridge physicist Hannah Fry’s door 'fan' trick — open a rear passenger window, then rapidly open and close the driver door several times — uses displaced air and short pressure differences to push hot air out of the car.
- The method cools the air you breathe but does not cool heat-soaked surfaces like seats, steering wheel, or dashboard, which will keep radiating heat until the AC or shade lowers their temperature.
- ADAC advises against immediately cranking the AC to maximum, recommends limiting the cabin–outside temperature gap to about 6°C, suggests running ventilation a few minutes after switching off AC to dry the system, and notes that for very short trips (around 5 km) open windows may be more fuel-efficient than air conditioning.
- Use the door trick carefully to avoid pinched fingers, be aware that very hot outside air will limit gains, and remember that parked interiors can reach extreme surface temperatures that pose burn and heat-stress risks to people and pets.