AC Not Cold when van not moving

What is your question?

Van has 17,000 miles. AC works fine as long as vehicle is moving. If you are parked w/running or not in constant motion(traffic)rear does not cool. It has dual air and dual controls. Also notice the external temp gage goes through the roof when sitting still.Kept climbing while parked up to 107 even though ac was on and then cooled once moving and temp went to 92 which was actually what it was outside. Dealer says it is just the way that it is w/ explorer conversion package.Does not seem right to me - too expensive (60,000 new) for that problem to exist. Bought for my special needs child and transport issues as many families do. S/N children most times cant take the heat and need the AC