What will happen if you leave a door open with air conditioner running?

Leaving a door open while running an air conditioner will cause the unit to work harder to maintain the desired temperature, as it continuously cools the warm air entering from outside. This can lead to increased energy consumption and higher electricity bills. Additionally, the effectiveness of the air conditioner may be compromised, resulting in a less comfortable indoor environment. Over time, this strain could also shorten the lifespan of the AC unit.