MARS definite purpose contactors are designed for use on refrigeration, air conditioning, and electric heating systems. They are available in one pole with shunt (one and one half pole) configurations, from 30 to 40A. MARS brand definite purpose contactors are also available in 2 pole models (30 And 40A) and 3 pole models (30 to 75A). The universal mounting base allows replacement of most contactor brands. Straight-through wiring and small size speeds installation. - Motors and Armatures (MARS) Definite Purpose Contactor.