When you use the AC with outside air circulation, the cooling will be slightly lesser than internal air recirculation because the AC has to be keep cooling the outside air which is generally warmer than the internally recirculated air.
But since you say that it gets warm enough to switch it off, you could check on the below 2 things first.
1. If there is any leak in the outside air suction point from the engine bay.
2. If the cold/warm air control is malfunctioning and letting the warm air to start mixing even in the cold mode.
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