Why does it stop cooling when I come to a stop

Hello, Does the air conditioner stop cooling, or does the engine stop cooling?

If you're talking about the engine cooling, it could likely be a cooling fan problem. If you're talking about the AC, then it could be a condenser, condenser fan, or a weak compressor. If the fan is working, then high & low side pressure readings need to be taken in order to isolate the problem.