DTC B1687-88: Engine Coolant Temperature Sensor Fault - CAN Signal: General Description
WARNING: This page is about a different car, the 2021 Kia Soul. However, it is still accessible from the selected car via links, so may be relevant.
In case of engine cold start, the A/C control module receives engine coolant temperature sensor signal through the CAN signal and the mode is changed to defrost by controlling the mode actuator.