What happens
Incorrect terminal correspondence, an interrupted conductor or unsuitable cable prevents reliable communication.
Typical symptoms
An indoor head responds locally but the system will not run, or communication faults recur after installation work.
Checks that distinguish this cause
With all relevant supplies safely isolated, match each terminal end to end against both diagrams and inspect the entire run. Separate loads before cable-integrity tests and compare cable specification and routing with the installed model requirements.
What can look similar
A missing outdoor power supply can make a healthy indoor unit report loss of communication.
Repair direction
Repair the proven cable or termination defect with the specified cable and connection method.
Verify the repair
Verify stable communication and correct operation through start, stop and all connected zones.
Equipment-specific limits
Some interconnect terminals carry line voltage or line-referenced signals. Wire count, terminal numbers, polarity, shielding and permitted splices are model-specific; do not treat a bus as R/C/Y wiring.
Practice this diagnosis
This cause is a reference topic; it does not yet have a dedicated simulated call. Browse the practice board.
References and applicability
Original HVACSim explanations with manufacturer and instrument-maker references for further reading. These resources support the subject; their model-specific examples are not specifications for every system.
- GREE: GREE communication-fault diagnostic guidanceA GREE-specific example of wiring and board fault isolation; E6 is not a universal code.
- Haier: Arctic Next Gen service manualAW/1U EH2VHD model examples of inverter, motor, sensor and circuit diagnostics; obtain the installed model manual.
Editorial review: 2026-09-29. Verify the current manual for the installed model.