(Technical Explanation & 859749-L Installation and Operation Manual Page References)

Fault Code 16 Description 

Climate Wizard CW‑H coolers use the PLC (Programmable Logic Controller) to communicate with external control systems such as:

• Multi‑Magic Wall Controller
• Building Management System (BMS)
• Modbus controller
• BACnet (MS/TP or IP) supervisor

These external systems send regular “check‑in” messages to the cooler. The cooler relies on these messages to know:

• what mode it should run in
• what fan speed to use
• whether cooling is allowed
• whether restrictions (lockouts) are applied

If these messages stop for more than 5 minutes, the cooler assumes communication has been lost and triggers Fault Code 16.

Because the cooler no longer knows what instructions to follow, the cooler cannot continue normal operation until communication is restored.

Expanded Technical Explanation

1. Why the Cooler Needs Communication

When under external control (WALL, BMS, MODBUS, BACNET), the PLC expects a continuous stream of control packets. These packets confirm:

• operating mode (VENT / IEC / DEC / SUPERCOOL)
• target fan speed
• enable/disable signals
• lock high/lock low commands
• Modbus/BACnet register activity
• Wall Controller network status

If these packets stop, the PLC has no valid instructions to continue operating.
Manual Reference: Fault Code 16 description — p.29

2. How Communication Works (RS‑485 or Ethernet)

RS‑485 (Wall Controller, Modbus, BACnet MS/TP)

• Uses a twisted‑pair cable (+ / –) plus GND
• Devices are “daisy‑chained”
• Cable shield must be grounded at one end only
• The system MUST have exactly two120Ω terminating resistors
  • one at the primary controller
  • one at the last cooler in the chain
    Manual Reference: RS‑485 wiring rules & termination — p.23

Ethernet (BACnet IP)

• Uses an RJ45 cable
• Requires correct IP address, gateway, subnet mask, and BACnet port
• Each cooler must have a unique Device ID
  Manual Reference: BACnet IP setup — p.22

3. What Communication Loss Causes Internally

When the PLC stops receiving external commands:

• It cannot confirm mode or speed
• It cannot respond to BMS outputs
• It cannot determine whether cooling is allowed
• It cannot verify lockouts
• It cannot update external systems on cooler status
• It pauses operation to prevent incorrect behaviour

Therefore, until communication returns,
the cooler cannot continue normal operation.

Manual Reference: Fault Code 16 behavior — p.29

4. Real‑World Causes Technicians Commonly See

• Loose RS‑485 terminal screws
• Reversed polarity (+/– swapped)
• Missing or extra terminators
• Cable shield grounded at both ends
• Broken RS‑485 cable at a bend or cable tie
• Duplicate Modbus/BACnet/Wall Controller addresses
• Wrong baud rate or parity
• Controller/BMS offline or rebooting
• BACnet network switch failure
• Modbus master not polling within 5 minutes
  Manual References:
• RS‑485 setup — p.23
• Modbus — p.21
• BACnet — p.22
• Wall Controller — p.20

Troubleshooting Procedure

1. Confirm Primary Control Method Setting

Ensure the cooler is set to the correct control source:

• WALL
• BMS
• MODBUS
• BACNET

If incorrect, the cooler will ignore the real controller.
Manual Reference: Control screen — p.18

2. Inspect RS‑485 Wiring (Most Common Cause)

Check:

• correct +/– polarity
• GND connected where required
• shield connected at ONE end only
• no star networks (must be daisy‑chain only)
• no crushed, split, or stretched cables
• correct cable type (shielded twisted pair, 120Ω characteristic impedance)

Manual Reference: RS‑485 rules — p.23

3. Check Terminating Resistors

Verify only these 2 terminators are installed:

1. At the primary controller (Wall Controller/BMS/Modbus master)
2. At the last cooler in the chain

All intermediate coolers MUST NOT have terminators.
Manual Reference: RS‑485 termination — p.23

4. Verify Node or Device Addressing

Wall Controller (RS-485)

• Each cooler: Node 1–15
  Manual Reference: p.20

Modbus (RS485)

• Each cooler: Address 1–99
  Manual Reference: p.21

BACnet MS/TP

• Unique Device ID (1–9999)
• Unique MAC (1–127)
  Manual Reference: p.22.

BACnet IP

• Unique Device ID
• Unique IP Address
  Manual Reference: p.22

Duplicate addresses = guaranteed communication instability.

5. Confirm Baud Rate & Parity Across All Devices

Common default:

• 38400 baud
• NULL parity

Every single device must match exactly.
Manual Reference: Modbus/BACnet/WC comms setup — pp.20–22

Remember:
Changing communication settings requires cooler power cycling.

6. Check Primary Controller Activity

The BMS/Modbus/BACnet/Wall Controller MUST send data packets at least every 5 minutes to avoid Fault 16.
Manual Reference: p.29

Check:

• Is the controller online?
• Is the BMS polling the cooler?
• Is the Modbus/BACnet master active?
• Are there network outages or switch faults?

7. Reset the Fault

After resolving the issue:

• Open ACTIVE FAULTS
• Press RESET
• If necessary, cycle power

Manual Reference: Fault reset — p.28

Manual Cross‑Reference Summary (Fault 16)