2000 Jeep Grand Cherokee air conditioner issues.?

We have been having issues with our Jeep overheating when sitting still...we are working on that...but now we are having a new problem we really want to get as many opinions on as possible. When sitting still, coming to a stop or at a drive thru, waiting to turn, etc., any time we come to a stop, the air starts blowing hot. When the Jeep is moving the air is super cold but when we stop it almost instantly turns hot. Any ideas? I've asked before but we always get just one answer and it is never the right one. Please, anyone, any opinion, we need some ideas. Thanks so much in advance for all the help we hope to get!