Error code
ACA
Meaning
The compressor controller isn't communicating properly
Critical
What to do
Why this happens
Possible causes include incorrect wire connections between the main and compressor inverter PBAs, disconnected wires between these components, or faults in either the main PBA communication circuit or the Compressor Inverter PBA communication circuit.
How to fix it
This one needs a professional technician — it involves the heat pump control system.
SourceSamsung service manual