Was it heating up before AC works or it started over heating after AC works ?
Seems your AC technician has not taken proper care of cooling system.
And to me it seems the engine is weak, it doesn’t has T-valve, its AC fan is not kicking in, ac compressor is weak, condensor is chocked or it has minor leak in the system.
Which city are you from. I know a person in Lahore who is master in fixing air conditions of older vehicles and turning them into proper ac works like new car.