Last week our 2001 T & C overheated and we had the thermostat replaced and they checked to be sure the fans were working, etc. Today my wife was driving the van to her mother's and called to inform me that the temp rose when she had the a/c on. When she turned the a/c off the temp went back to normal. What is the possible issue in this case?

 

that sounds like a fan issue or the radiator is clogged up