How do you adjust Nissan 4.2 diesel engine air conditioning drive belt?

To adjust the air conditioning drive belt on a Nissan 4.2 diesel engine, first, locate the belt tensioner and loosen the tensioner bolt. Then, adjust the position of the tensioner to achieve the desired belt tension, ensuring there is about a half-inch of deflection when pressing down on the belt at its longest span. Once the desired tension is achieved, retighten the tensioner bolt and check the belt alignment. Finally, start the engine to verify that the belt operates smoothly without slipping.