Check all the belts & pipes. If need to change, then do it.
Most of the ACs dont work good in idle cars. Unluckily that includes my monster too.
When driving, it works like Chill. But at idling its efficiency is less.
And reason for this happening is Compressor gets weaker and it start taking more load from engine.
You can keep it running if you wish. Or slightly push down your foot on gas padel on idling but don’t ignore the heat guage while doing so.