it'll be the gas getting too hot and the overload thing cutting in

forgin rs is the man to speak to about how technical stuff works on ac as he's the expert, but for starters check to see that the fan works to cool the condenser down (or is it called the evaporator? don't know, the rad in front of the rad)

it could also be the compressor on it's last legs as it might be worn and not sending the gas around the system

in my case it was the compressor electric clutch that had packed up and when it got too hot it wouldn't work

so a few options to try out before calling in the a team