DTC U0164: Lost Communication With HVAC Control Module
WARNING: This page is about a different car, the 2022 Subaru WRX. However, it is still accessible from the selected car via links, so may be relevant.
DTC detecting condition:
Detected when CAN data is not received from A/C Control Module.
NOTE:
Perform the diagnosis for LAN system. Ref. to LAN SYSTEM (DIAGNOSTICS)>BASIC DIAGNOSTIC PROCEDURE>PROCEDURE