Equipment Interface Module controls up to 4-stages of heat and 2-stages of cool in a heat pump system and up to 3-stages of heat and 2-stages of cool in a conventional system. Three sets of Universal IAQ contacts to control humidification, dehumidification, and ventilation. Four sensor inputs for wired sensors or dry contact devices. Used with all versions of Prestige IAQ Thermostats and the New RedLINK VisionPRO Thermostats. Used with All THX9421R5021 Prestige® 2-Wire IAQ Thermostats and all versions of Prestige® IAQ Thermostats and the VisionPRO® Thermostats with RedLINK™ technology.