Get in your car, crank A/C, and proceed to open and close the door once a minute. The interior of the car will remain a lot cooler than the outside air. Just because UPS says different, doesn't mean people should be parrots. Do you think you're evacuating a massive volume of air in your package car by opening a door every two minutes? A/Cs would remain largely effective in package cars, even with engine stops. This company has many people brainwashed against their best interests. The reality is people are petrified that any money spent by the company will affect their wages and pensions. They've got some of you dancing on a tightrope. That said, better ventilation in the rear would go a long way.