overheating with A/C on...I'm so confused!

[Buford]

Okay,

Why is it that if I us my 71 2500 GMC with the camper and pulling the boat without the A/C is will not over heat. I've driven that truck all day in the summer and it runs around 190-195 totally loaded. Now, when the truck is not loaded at all, running empty, and I turn on the A/C the temperature will climb up to 215. I usually shut it off by then and it will go down to about 185. I can't imagine the A/C putting on a greater load on the engine than the camper and boat. I am running the A/C cooler in front of the radiator (along with the trans. cooler). Could it be that when the A/C is running the air that is normally cooling the radiator is being heated by the A/C cooler? I don't know, so posting this quandry to you guys.

Thanks!
Aaron