98 Accord temp problems. PLEASE HELP

I have a 98 accord ex v-6 with 149000 miles. I have owned the vehicle for 6 years, with no problems. Recently when the car is being driven during the heat of the daytime, the temp guage will go up and the a/c will stop blowing cool air. If I turn the a/c off the temp slowly goes back to the normal range. I do not have this problem when it is cool out. I decided to change and flush the coolant system as well as install a new thermostat. I did both of those things and the car is still doing the same thing. Can the a/c put that much strain on the engine to make it run hot? The car runs great if the air is off, I do seem to notice that the car is not as strong with the a/c on, it seems to loose some power, and I don't remember it being this way in the past. Any ideas I would really appreciate it!
Matt