We have a sled dog team and purchased a 2012 GMC Savana, pulled out the seats then added wire dog kennels to transport them. This question involves air-conditioning since we don’t want hotdogs. Traveling on the highway during the summer in 90 degree plus weather the air conditioning works fine and cools to 35 degrees plus or minus out the vents (We have a thermometer on a vent). When we stop at a rest stop to potty the dogs we leave the engine running and the air conditioning on to keep them cool. Almost immediately the air blowing from the vents starts rising to 70 degrees. My 2012 Ford Explorer does not have this issue and holds a steady cool temperature while at idle. Our dealer added dye found a leak and it was repaired so the system is topped off and the problem has persisted. Any ideas where to look next such as failed switches or compressor problems and what a dealer needs to do to make a repair. They feel the air conditioning is preforming well.