These selections provide the logic to control a Preheat coil. A Preheat coil may be located in the Outdoor Air Duct (ahead of the mixing plenum). If this is the case, a Preheat coil is always set to Control to Preheat Air Temperature. When in the Mixed Air Duct, the coil may either be controlled by a dedicated sensor or sequenced with the other devices. During startup, if a DA-T or PH-T sensor is available, the Preheat coil is controlled by the LT-SP (Low Limit Setpoint).