VRF Commissioning Procedure (MCHX & MCRX)

⚠️ Safety Notice – Reverse Cycle Air Conditioners

This equipment must only be installed, commissioned, serviced and repaired by suitably qualified and licensed personnel.

Before commencing work, complete a task-specific risk assessment and ensure electrical isolation procedures, safe access, adequate service clearances and appropriate PPE have been considered. All work must comply with applicable regulations, standards and manufacturer requirements.

Particular care must be taken when working around electrical systems, refrigerant circuits, moving parts, roof spaces, ceiling spaces, confined spaces and working-at-heights hazards where applicable.

Do not proceed if safe access, required clearances, confined space risks or appropriate safety controls cannot be achieved and maintained.

Safety takes priority over diagnosis, repairs, installation schedules and customer expectations. If the task cannot be completed safely, it must not proceed until the risks have been adequately controlled.

TABLE OF CONTENTS

Quick Navigation
- Overview
Before Starting Commissioning
What Does A0 Mean?
Common Reasons A0 Does Not Appear
Communication Wiring Requirements
120Ω Communication Resistor
Refrigerant Requirements
Y-Branch Installation
Start Commissioning
Debugging Sequence
Technician Action Required During Commissioning
- Step 03 – Outdoor Quantity
- Step 04 – Indoor Quantity
Commissioning Fault Codes & Corrective Actions
- CC
- CF
- L7
- C2
- C3
- CH
- CL
- U0
- U4
- U6
- U8
- U9
Most Common Commissioning Failures
Successful Commissioning
Technician Sign-Off Checklist

Overview

This article explains how to commission Braemar VRF systems after installation has been completed.

Applicable to:

MCHX Heat Pump VRF
MCRX Heat Recovery VRF

Useful Links to helpful solutions: -

Braemar VRF Outdoor Units – AO / A0 "ready for debugging" Debugging, Commissioning & Troubleshooting Guide (Installation & Startup Requirements)

VRF REVERSE CYCLE SERVICE AND INSTALLATION

Before Starting Commissioning

Before commissioning, ensure:

✅ Pipework completed

✅ Drainage completed

✅ Electrical wiring completed

✅ Controllers installed

✅ Communication wiring completed

✅ Refrigerant charge calculated

✅ Pressure test completed

✅ Vacuum completed to 500 microns

✅ Service valves opened

✅ Additional refrigerant added

✅ Outdoor unit powered for minimum 8 hours

✅ All indoor units powered

✅ Outdoor unit displaying A0

Outdoor unit display showing A0, indicating the VRF system is ready for commissioning.

⚠️ CRITICAL: COMPRESSOR PREHEAT REQUIRED

Do NOT start VRF commissioning until the outdoor unit has been powered continuously for a minimum of 8 hours.

The compressor crankcase heater requires at least 8 hours of power to warm the compressor oil before startup. Attempting to commission the system too early may result in:

U0 - Compressor Not Preheated
Commissioning stopping at Step 08
Potential compressor damage
Unnecessary service callbacks

Before Pressing SW7, Confirm:

✅ Outdoor unit powered for 8+ hours

✅ Indoor units powered

✅ Outdoor display shows A0

✅ No active fault codes displayed

If U0 Appears During Commissioning

The system has not completed the required preheat period.

Action:

Stop commissioning.
Leave power applied to the system.
Wait until the full 8-hour preheat period has elapsed.
Restart the commissioning procedure.

Technician Tip: Where possible, energise the VRF system the day before commissioning to avoid delays on site.

⚠️ CRITICAL: 120Ω RESISTOR REQUIRED

Do NOT start commissioning until the supplied 120Ω resistor is installed across D1 and D2 on the last indoor unit.

A missing resistor is one of the most common causes of VRF commissioning failure and can result in:

Indoor units not being detected
Communication faults
Incorrect indoor unit count
Commissioning failure

Before Pressing SW7

✅ 120Ω resistor fitted across D1 and D2 on the last indoor unit

✅ Communication wiring daisy-chained

✅ D1 connected to D1 and D2 connected to D2 throughout the system

✅ No star wiring

Systems with a Central Controller: Fit an additional 120Ω resistor across G1 and G2.

Technician Tip: If the indoor unit count is incorrect during commissioning, check the resistor installation before investigating other faults.

What Does A0 Mean?

A0 means:

System Not Debugged

The outdoor unit has:

Powered successfully
Established communications
Detected indoor units
Is ready to commence commissioning

Do not attempt commissioning unless A0 is displayed.

Common Reasons A0 Does Not Appear

If A0 is not shown, check:

Power Supply

All indoor units powered.
Outdoor unit powered.

Communication Wiring

D1 connected to D1.
D2 connected to D2.
No crossed conductors.

Resistor Installed

120Ω resistor fitted to last indoor unit.

Existing Faults

Resolve any displayed fault codes first.

Communication Wiring Requirements

All communication wiring must be:

Daisy chained
D1 to D1
D2 to D2
Shielded cable
Shield earthed at one end only

Never wire communications in a star configuration.

Circuit	What it does	How to wire it
D1 / D2	Outdoor ↔ Indoor communication	Daisy chain all indoor units
H1 / H2	Wall controller ↔ Indoor units	Daisy chain to all controlled units

Correct VRF D1-D2 daisy-chain communication arrangement.

120Ω Communication Resistor

Each VRF system requires a terminating resistor.

Install the supplied 120Ω resistor:

Across:

D1 and D2

On:

The last indoor unit in the communication network

If a central controller is installed:

Install an additional resistor across:

G1 and G2

120Ω resistor installation on the final indoor unit.

Refrigerant Requirements

Commissioning will fail if insufficient refrigerant has been added.

Before commissioning:

✅ Additional refrigerant calculated

✅ Additional refrigerant added

✅ Pressure test complete

✅ Vacuum complete

✅ Minimum 70% of calculated refrigerant added

Common result:

U4 – Refrigerant Shortage

Y-Branch Installation

Incorrect Y-Branch installation can cause:

U8 faults
Poor performance
Failed commissioning

Requirements:

✅ Installed within ±30°

✅ Insulated

✅ Supported correctly

✅ Minimum 500 mm straight pipe

Correct Y-Branch installation requirements.

Start Commissioning

Step 1

Confirm all displays show:

Step 2

Configure one outdoor unit as:

MASTER UNIT

Only one master unit is permitted.

Step 3

Locate outdoor unit displaying:

Step 4

Press and hold:

SW7

For approximately:

5 seconds

The outdoor unit enters debugging mode.

Debugging Sequence

The system automatically performs the following checks:

Step	Function
01	Master unit verification
02	Address allocation
03	Outdoor quantity check
04	Indoor quantity check
05	Communication test
06	Outdoor component test
07	Indoor component test
08	Compressor preheat check
09	Refrigerant level check
10	Valve status check
11	Refrigerant verification
12	Final startup confirmation
15	Cooling debug
16	Heating debug
17	Completion

Technician Action Required During Commissioning

Step 03 – Outdoor Quantity

System displays number of outdoor units detected.

Verify quantity matches installation.

Press:

SW7

to continue.

Step 04 – Indoor Quantity

System displays number of indoor units detected.

Verify quantity matches installation.

Press:

SW7

to continue.

If quantity is incorrect:

Check:

Indoor power.
Communications.
Resistor.
Wiring polarity.

Commissioning Fault Codes & Corrective Actions

CC

No Master Outdoor Unit

Check:

Master unit selection.

CF

Multiple Master Units

Check:

Only one master unit configured.

L7

No Master Indoor Unit

Check:

Indoor communications.
Indoor power.

C2

Compressor Communication Fault

Check:

Compressor inverter wiring.
PCB connections.

C3

Fan Communication Fault

Check:

Fan wiring.
Outdoor PCB.

CH

Indoor Capacity Too High

Check:

Indoor unit selections.

CL

Indoor Capacity Too Low

Check:

Indoor unit selections.

U0

Compressor Not Preheated

Check:

Outdoor unit powered for minimum 8 hours.

U4

Insufficient Refrigerant

Check:

Refrigerant charge.
Leaks.
Refrigerant calculations.

U6

Outdoor Valves Not Open

Check:

Liquid valve.
Gas valve.
Oil balancing valves.

U8

Indoor Pipework Fault

Check:

Y-Branches.
Pipe sizing.
Pipe routing.
Crossed pipework.

U9

Outdoor Pipework / Valve Fault

Check:

Outdoor pipework.
Service valves.
Oil balance valves.

Most Common Commissioning Failures

Missing 120Ω resistor.
Communication wiring not daisy chained.
Indoor units not powered.
Refrigerant not added.
Outdoor powered less than 8 hours.
Closed service valves.
Incorrect indoor count detected.
Star-wired communications.
Crossed refrigerant pipework.
Incorrect master unit setup.

Successful Commissioning

Commissioning is complete when the outdoor unit displays:

1 OF OF

This indicates:

✅ The commissioning (debugging) process completed successfully

✅ All indoor and outdoor units were detected correctly

✅ Communication checks passed

✅ Refrigerant and valve status checks were completed

✅ No commissioning faults were detected

✅ The system has returned to standby mode and is ready for normal operation

Important: Successful commissioning does not replace a final operational check. After commissioning, operate the system and confirm all indoor units, controllers, cooling and heating functions are operating correctly before leaving site.

Technician Sign-Off Checklist

Installation

☐ Pipework complete

☐ Drainage complete

☐ Controls installed

☐ Communication wiring complete

☐ Resistor fitted

Refrigeration

☐ Pressure tested

☐ Vacuum below 500 microns

☐ Refrigerant added

☐ Service valves opened

Power

☐ Indoor units powered

☐ Outdoor unit powered minimum 8 hours

☐ A0 displayed

Commissioning

☐ Outdoor quantity confirmed

☐ Indoor quantity confirmed

☐ OF OF displayed

☐ Cooling tested

☐ Heating tested

Handover

☐ Customer instructed on operation

☐ Warranty registration completed

MCHX VRF Commissioning procedure - A0 System is not debugged