Applies to

  • Multi head outdoor units with multiple flare ports labelled A, B, C (and D where applicable)

  • Known recent example reported: AOTH30KBTA4 

Issue Summary

The install manual’s guidance for multi-head port connection order is located in the Flare connection section and can be missed during installation.

Where pipework is connected to B and C (with no indoor connected to A), the system may operate but can present reduced capacity and compressor not ramping up correctly, particularly when only one indoor unit is running.

This has been observed in multiple field cases and is likely under-reported.

Symptoms

  • Poor heating/cooling performance compared to expected capacity

  • Compressor does not ramp up appropriately under load

  • System appears “lazy” or underpowered when only one indoor is on

  • May present as “installation / capacity” complaint rather than a hard fault code

Root Cause

On multi-head systems, the outdoor unit ports are not interchangeable in the way installers may assume. The manual specifies that indoor units must be connected in port order (typically A, then B, then C, then D), and any unused ports must be closed.

When the first connected indoor is not on port A, the system can behave abnormally and limit performance.

Manual note (commonly missed): “When connecting the indoor unit, it should be connected in the order of port A, B, C, and so on. Please be sure to close remaining unconnected ports so that they do not leak refrigerant.”

Confirmation / Diagnostic Checks

1) Confirm port usage against outdoor unit markings

  • Visually confirm which ports are used (A/B/C/…)

  • Check if any indoor is connected to port A

  • Confirm unused ports are properly capped/closed

2) Confirm indoor unit capacities and locations (example case)

  • Example reported: 24 (lounge) + 09 (bedroom) connected to B and C, A unused

  • Symptom: system not ramping well with only one indoor operating

3) Performance validation

If port order is incorrect, the quickest “proof” is to correct the port order and re-test:

  • Run a single indoor at demand and confirm compressor ramps and capacity improves.

Corrective Action

Mandatory installation correction

  1. Recover refrigerant in accordance with policy and regulations.

  2. Reconnect pipework so the first indoor is on port A, then next on B, then C, etc.

  3. Ensure all unused ports are sealed/closed (caps installed correctly).

  4. Evacuate, leak test, and recharge per installation requirements.

  5. Recommission and verify correct operation and performance.

Important: Do not leave port A unused if there are connected indoor units on higher ports.


Verification After Correction

  • With one indoor unit running at high demand, confirm:

    • Compressor ramps appropriately

    • Supply air temperature / capacity aligns with expected performance

    • No abnormal cycling or sustained low output

Prevention / Installer Guidance

  • During installation briefing, call out that the port order requirement is located in the Flare section of the manual.

  • Add a job checklist step:

    • “Confirm multi-head indoor connections are in A → B → C order; confirm unused ports closed.”