overheating with ac

I have a 2002 GT-S with 126 K that i bought few weeks ago. Today it started to overheat only when the AC is running. As soon as you turn the AC off, the temperature goes back to normal. Checked for any kind of leaks, which there are none. The cooling fan is working with no issues as far as i can see, and the coolant level is okay.
If i put the AC on the temperature goes all the way to H and is flashing within a few minutes.
I have no clue where to start, thermostat, etc... Does anyone have any idea what could be the problem?

Thanks in advance!!