when driving the engine temp goes up to 120 C when the air is on

It could be many things, unfortunately and without experiencing the problem first hand or being able to do some basic diagnostic tests its hard to say. It could be a weak fan clutch, a thermostat that is not fully opening, a restricted radiator (not allowing coolant to circulate through all the cooling tubs of the radiator) or even the possibility of a mildly blown head gasket. Hard to tell without being able to do some basic tests.

Patrick hit the nail on the head. I would recommend having your vehicle diagnosed sooner rather than later to avoid damaging any other components.