Aprilaire #4851 Blower Activation Relay.

• For Aprilaire series 500, 600, and 700 humidifiers that use the Automatic Digital Humidifier Controls (# 56 and # 58).

• Allows digital control (#58) to turn on system fan when there is a call for humidification (but not heat).

• This device will initiate HVAC fan operation when there is a call for humidity, even when there is no heat call.

• Use this relay in applications where humidifier operation is required beyond a call for heat, e.g. when installed on a heat pump or during times of the year where there is a need for humidity but not a need for heat.