Need help guys, newbie to cars.

I did not use my car for 1 week because I went to the province. When i came back and used it, i noticed that the temp gauge which normally settles at midpoint even during long drives rose to around 3/4 of the gauge. So i turned off the aircon and it helped. however whenever i use the aircon, the temp gauge rises to almost 3/4 but not to the red line yet. this is the first time that the temp gauge rose to that level. what could be the problem?