TheHRC-4DE-DIG staging relay is intended for use with the YB slave output on the HTC DIGITAL range of controllers. This module offers 2 stages of Heat and 2 stages of Cool , and also incorporates a Modulating Economy Cycle Output with a Comparitor Override. This output is produced by comparing the outside air temperature to either the return air or room temperatures. If theHRC-4DE-DIGis in the cooling mode and the outside air is lower than the room/return air temperature the Economy Cycle output will start modulating.