2002 SEAT Ibiza AC SOMETIMES WORKS AND SOMETIMES DOESN'T!

My AC works fine when the temperature outside is not to hot. When the weather temperature is under 90 °f the AC works fine, in fact I plug a pressure guage at the high terminal of the ac system, and it was about 300 psi, but when the weather temperature is over 100 °F the AC system start to fail, it works and then stops. The pressure in the high terminal rises over 390 psi and then it stops. When it cools down, the pressure falls and the it starts again, but the pressure raises again and it stops once again. My car has two fans for the radiator and the ac system, and they work fine,
So what could be the problem. I appreciate your help. Thank you.