In 2017, the VRF units were upgraded to a new PCB which includes new firmware. There may be a scenario when you will be required to update the firmware for an indoor unit. This will be based on whether you have a mixture of old and new products installed within the system. The "VRF Firmware Upgrade Path" document will show whether a firmware upgrade is required. A new ODU model number will have a "C" in the 9th digit and the MCU will be a 4MCUT. The document also includes new Indoor Model numbers to confirm if the IDU is a new model. If you are required to upgrade the ODU firmware based on the chart, you will not be able to upgrade firmware due to board compatibility. Two boards will have to be replaced in the ODU's; (1) Main PCB part # BRD06096 and (2) HUB PCB part # BRD05482 . NOTE: make sure to save EEPROM of and plug it in to the new main PCB. All of the new indoor unit firmware are attached in this case solution. Update: The 3rd generation firmware file is for Highwall units with a "D" in the 9th digit.