Seeley International Pty Ltd

Purpose

This article explains how to correctly connect a CE52 Central Controller when a VRF system has ONE Outdoor Unit (ODU).

It also explains:

• What the D1 / D2 daisy chain is
• How the CE52 interacts with it
• Why two wiring options are allowed for single‑ODU systems only

What Is the D1 / D2 Daisy Chain?

• D1 and D2 are the communication terminals used to link Indoor Units (IDUs) together
• Indoor units are wired IDU → IDU → IDU in a straight line (daisy chain)
• The chain has:
  • A first indoor unit
  • A last indoor unit
• The last indoor unit is where controllers or termination resistors are connected

✅ This D1/D2 chain exists on all VRF systems, regardless of how many outdoor units are fitted.

⚠️ Important:

• Star or radial wiring is NOT permitted
• Communication wiring must not run from the outdoor unit to each indoor unit individually
• The D1/D2 network must always be installed in series (daisy‑chain only)

Single Outdoor Unit

✅ When there is ONE Outdoor Unit, the CE52 can be connected in either of the following ways:

• Via the Indoor Unit D1 / D2 daisy chain
• Directly to the Outdoor Unit G1 / G2 terminals

✅ Both options are valid ONLY when there is a single ODU

Option 1 (Most Common) – CE52 Connected to the D1 / D2 Daisy Chain

What this means:

• Indoor units are already linked together via D1/D2
• The CE52 connects to D1 and D2 on the LAST indoor unit

In simple terms:
The CE52 joins the same communication wiring that all indoor units are using.

Important points:

• The CE52 does NOT connect in the middle of the chain
• It always connects at the end
• A matching (120-ohm termination) resistor must be connected to G1 / G2 at the CE52

✅ This is the most common and simplest method

⚠️ Critical wiring rules:

• Only ONE termination resistor is permitted on the communication network
• The resistor supplied in the outdoor unit pack‑out kit must be used

Option 2 – CE52 Connected Directly to the Outdoor Unit (G1 / G2)

What this means:

• The CE52 does not connect to the D1/D2 wiring
• It connects directly to G1 / G2 on the Outdoor Unit

⚠️ Critical clarification about D1 / D2:

• Even though the CE52 is connected to G1/G2, the indoor D1/D2 daisy chain still exists
• Indoor units MUST still be wired IDU → IDU in series
• Star configurations remain prohibited

✅ When using this method:

• The termination resistor must be installed on D1 / D2 of the LAST indoor unit

✅ This option is ONLY allowed when there is ONE ODU

Why Both Options Work (Single ODU)

With only one outdoor unit:

• The indoor (D1/D2) and outdoor (G1/G2) networks are treated as one system
• The CE52 can communicate from either end

Common Single‑ODU Mistakes

❌ CE52 connected mid‑way along D1/D2
❌ Star or radial communication wiring
❌ No termination resistor fitted
❌ Termination resistor fitted at multiple locations
❌ Communication cable screen not earthed correctly

CE52 Central Controller Connections

Additional Terminal Functions

• F1 / F2

  • Used for Fire Trip shutdown input
  • Typically connected to:
    • Fire Control Panels
    • Commercial / industrial fire systems

Power Supply & Wiring

Installation and wiring must be done by a qualified electrician.

Power Requirements

• Uses standard household power (240 V AC)
• Works with 50 or 60 Hz
• Only use an approved 3‑wire power cable
• Cable size: 1.5 mm²
• Must meet electrical safety standards

Connecting the Wires

• Connect the communication wires to terminals G1 and G2
• Option 1 only: Fit the supplied 120 -ohm resistor across G1 and G2
• Connect Neutral to N
• Connect Live to L
• Connect Earth to the earth terminal on the metal box cover

✅ Ensure all screws and terminals are tight before power‑up

Termination Resistor – Mandatory Requirement

Resistor must be connected to G1 / G2 (Option 1)

⚠️ IMPORTANT – Option 2:

• Fit the 120-ohm termination resistor across D1 / D2 of the LAST indoor unit

✅ Every communication network gets:

• ONE termination resistor
• Fitted ONLY at the far end
• Never more than one

✅ The “far end” depends on where the CE52 is connected

Communication Cable Screen (Earth) – Critical

• Use shielded, twisted‑pair communication cable
• The cable screen (drain wire) must be:
  • Earthed at ONE point only (typically at the outdoor unit)
• Do NOT earth the screen at multiple locations

⚠️ Incorrect screen earthing can cause:

• Communication dropouts
• Random indoor unit faults
• CE52 offline alarms