E6 – Communication Error

Communication fault between Indoor PCB and Outdoor PCB
Applies to:

• SDHV / KDHV ducted systems
• SACV / KACV “Invertair” add-on coolers

Key Point

• The indoor PCB supplies communication voltage to the outdoor PCB via terminals 1 and 2
• The outdoor PCB may show LED lights even without 240V power — this is normal

Main Check Points

Communication Cable

• Must be:

  • Twin cable approx. 0.75mm
  • Maximum length 100m

• Ensure cable is:

  • Continuous (no breaks)
  • Correctly terminated at both ends

IMPORTANT – Cable Routing (Critical)

Communication cable (terminals 1 & 2) must NOT be run with 240V mains cables

• Do NOT run in the same conduit, tray, or loom as mains wiring
• Do NOT cable-tie comms cable to 240V cables

This can cause:

• E6 communication faults
• Signal interference
• Intermittent or hard-to-diagnose issues

If suspected:

• Physically separate comms cable from mains wiring
• Re-test communication voltage at both indoor and outdoor

Check Communication Voltage (Wall Controller ON)

Measure across terminals 1 and 2 (terminal-to-terminal, NOT to earth or neutral):

• At the indoor unit terminal block, and
• At the outdoor unit terminal block

Expected readings:

• 7–12 VAC (fluctuating)
• 6–24 VDC

What This Confirms

• If you get the correct reading at one end, you should get the same reading at the other end
  • Same at both = cable OK
  • Voltage at one end only = cable fault (break or loose connection)

Important Notes

• Voltage is supplied from the indoor PCB
• Fluctuating readings are normal
• No voltage will be present if the wall controller is OFF

Outdoor Power Check

• Confirm 240V supply at outdoor unit:
  • L1 to N1 = 240V
  • L1 to Earth = 240V

If There Is NO Voltage on Terminals 1 & 2

Follow these steps:

1. Check indoor unit power

   • Confirm correct voltage
   • Check breaker and isolator

2. Check indoor PCB fuse

   • Replace if blown
   • If it blows again → possible PCB or wiring issue

3. Check indoor PCB output

   • If unit has power but no comms voltage → indoor PCB likely faulty

4. Check communication cable

   • Perform continuity test
   • Inspect for breaks or loose wiring

Practical Fault-Finding (Field Checks)

Wall Controller

• Confirm correct model
• Check for faults
• ❗ Incorrect or faulty controllers can cause E6

Indoor Fan Test

• Run system in Fan Only mode
  • Fan runs → indoor unit likely OK
  • Most faults will be outdoor unit or communication wiring

PCB Inspection

Check indoor and outdoor boards for:

• Blown fuses
• Burn marks (top and underside)
• Rodent or insect damage
• Corrosion

Wiring Checks

• Confirm:
  • No broken wires
  • Tight terminals
  • Correct connections

Power Supply Quality

Check at both units:

• Active to Neutral
• Neutral to Earth

Poor Neutral or Earth can cause communication faults

Customer Questions

Ask if there have been:

• Recent electrical works (solar, switchboard changes)
• Power surges

Dedicated Circuit

• System must be on a dedicated circuit
• No other equipment sharing the supply

Third-Party Devices

• Disconnect:

  • Zone systems
  • Third-party controllers

• Retest system

Invertair Add-On Cooler Specific Checks

• DO NOT connect 24V from TQ heater to terminals 1 & 2

  • This will damage indoor or outdoor PCB

• Invertair add-on coolers are only compatible with TQ heaters using:

  • The correct supplied cable
  • Connected to the COM port on heater board