TORONTO, Ont. — Admit it. A truck’s air system probably isn’t your most pressing maintenance concern. The systems are pretty reliable, and beyond changing the air-dryer desiccant cartridge every couple of years, you probably don’t give the rest of the system any more attention than it absolutely needs. While its primary function is supplying air for the brake system — an important task in its own right — other components on the truck need air, too. Automated transmissions, for example, and certain emissions system components.