1994 Jeep Cherokee Car does not start in hot weather

Hopefully you will be able to give me some insight into this problem because I dread driving when the hot weather comes. I drive a 1994 Jeep Grand Cherokee with 70,000 mis. I usually never have a problem with my car until summer hot weather comes and then it has problems starting. It is not every day that I experience the starting problem it seems to happen after I have driven to several different places and when I return to the car if it is parked in the sun (I always try to find a spot with enough shade to cover the engine and that seems to work) and try to start it the engine will not turn over. I will try to start it several times but no luck. The weird thing is after I try to start it and it does not work I roll down all of the windows, open the car doors (let in fresh air) and wait 10 or 15 minutes it will almost always start up. I have asked the dealership several times what it could be and even taken the car in but they said that they did not know unless it was actually not working at that time. So twice when it did not start I had it towed to the dealership and of course by the time my car arrived on the tow truck and they got around to starting it the car would start. Very frustrating. It's like it needs to cool down because it is to hot to start. Have you heard of this problem before (I hope so) or do you have any idea what it can be? Thanks for any info you can give me.