The MP15AC is 1.5 ft (457 mm) longer than an MP15DC, the extra space being needed for the rectifier equipment.

The alternator-rectifier combination is more reliable than a generator, and this equipment became the standard for new diesel-electric locomotive designs.

Instead of the front-mounted radiator intake and belt-driven fan used on all previous EMD switchers, these have intakes on the lower forward nose sides and electric fans.

Side intakes allowed the unit to take in cooler air, and the electric fans improved a serious reliability issue found in its earlier DC sisters.

[1] [5] The six largest buyers, Milwaukee (64), Southern Pacific (58), Seaboard Coast Line Railroad (45), Nacionales de México (25), Long Island (23), and Louisville & Nashville (10), were all buying road locomotives with AR10 alternators throughout the 1970s, so the similarly equipped MP15AC was easily kept in good repair.