Increase Year-Round Comfort and Operating Efficiency The Taco Hydro Air Fan Control is the ideal interface between the thermostat and air handler that will increase year-round comfort and operating efficiency in your systems. The Hydro Air Fan Control also includes an isolated end switch to start the boiler or pump. When the thermostat calls for heat, the Fan Control energizes the end switch relay and allows the fan to operate at low speed when the water is above the aquastat setting. When the thermostat calls for cooling, the Fan Control energizes the condenser and operates on high speed. In addition to standard features, the HAFC201 Model also includes three built-in fan time delay options, two selectable pump exercise modes, a secondary aquastat connector for freeze protection and the ability to switch a pump and/or boiler.