Why does my A/C work inconsistently?

When it’s hot outside, and I turn my A/C on max cool, the air will blow hot for 10-12 minutes, and will not start cooling down until 10-12 minutes of driving. It’s very sporadic. But then ones it starts, if you stop at a red light, it will get hot again. The Freon pressure is normal/high. Any tips to troubleshoot?