Police spokesman Sgt. Tommy Thompson says 28-year-old Travis Ward took the vehicle, which was unlocked and had its keys in the ignition. It had been left running early Sunday to keep cool for anyone seeking medical care.
Thompson says Ward drove the ambulance for a few blocks, striking a post, a fence and parked cars. He says the man told police he had used marijuana before the incident.
Thompson says no injuries were reported and he wasn't aware that anyone at the west Phoenix fire needed medical care.
Ward was booked on suspicion of theft and criminal damage. It was not immediately known whether he has a lawyer.