Swapping to Hive thermostat. 4 wire communicator has 2 wires per post
Leave the wires to the heatpump where they are at

Your system, instead of running Y, O/B, and C wires to the outdoor unit to control it, simply puts the compressor controller on the same ABCD bus that is used to connect the indoor unit to the matching (communicating) thermostat.  As a result, when you remove the thermostat wires from the ABCD bus, you need to leave the wires to the heatpump in place, so that the indoor and outdoor units can talk to each other.