LG Heat Pump Error Code CH39

CH39 indicates a transmission error between the PFC Micom and the INV Micom, which are two microcontrollers located on the inverter PCB assembly. These chips must communicate continuously to manage power conditioning and compressor motor control. When that communication fails, the system logs CH39 and halts normal operation. The fault is most often caused by a software version mismatch or a hardware failure on the inverter board.

When CH39 is active, the heat pump will typically shut down compressor operation to protect the system, so continued operation in a normal heating or cooling capacity is not likely possible. Attempting to force the unit to run with an active inverter communication fault risks further damage to the PCB or compressor. It is best to leave the unit off and have it serviced promptly.

Repair costs vary depending on whether the fix is a software correction or a full inverter PCB assembly replacement. A software version check and correction by a technician may involve a service call fee in the range of $75 to $150. If the inverter PCB assembly requires replacement, parts and labor combined can range from $400 to $900 or more depending on the specific unit model and local labor rates.

This fault requires verifying the firmware versions of internal microcontrollers, which is not a task that can be performed without proper diagnostic tools and technical knowledge. If the software versions do not match, a qualified technician will need to update them. If the inverter PCB assembly has failed, it will need to be replaced by someone trained to work safely with high-voltage inverter components.

A power reset may temporarily clear the fault display, but if the underlying cause, such as a software mismatch or a failing inverter PCB, has not been addressed, the error will return once the system attempts to operate again. A reset is not a repair and should only be used as part of a diagnostic process, not as a solution.