General Assist Technical Reference

VRF - Changing a Master Unit to a Slave

Temporarily removing a failed outdoor unit from a multi-outdoor refrigerant system
For VRF systems using two or three outdoor units on the same refrigerant circuit.
If a system has two or three outdoor units on the same refrigerant circuit and one outdoor unit must be removed temporarily due to a failure, the transmission wiring and outdoor-unit DIP switch settings must be changed so the remaining equipment can operate with the correct master/slave configuration.
Qualified technicians only: Isolate electrical power before changing transmission wiring or DIP switch settings. The failed outdoor unit must be electrically disconnected and its service valves closed before the system is operated in the temporary configuration.

1. Change the transmission wiring

If the original MASTER outdoor unit has failed, it must be removed electrically from the transmission network. The first remaining slave outdoor unit then becomes the new master.

Depending on the system configuration, the transmission wiring to the new master will need to be connected to:

  • X1 / X2 for transmission to the indoor units; or
  • Z1 / Z2 where the transmission continues to other refrigerant systems.
Typical example: The original master is connected to the indoor-unit transmission network, while Slave 1 and Slave 2 are linked through the outdoor-unit transmission connections.
Original master and slave outdoor unit transmission wiring

To operate with the failed master removed, electrically disconnect the failed master and reconnect the transmission so that Slave 1 becomes the new MASTER.

Transmission wiring after the first slave becomes the new master

2. Set the outdoor unit addresses - DIP SW SET3-1 and SET3-2

Set the outdoor-unit address switches so each operating outdoor unit has the correct master/slave address.

Outdoor unit roleAddressSET3-1SET3-2
Master0OFFOFF
Slave 11OFFON
Slave 22ONOFF
Outdoor unit address DIP switch settings

3. Set the number of slave units - DIP SW SET3-3 and SET3-4

If an outdoor unit is electrically disconnected from the refrigerant system, the new MASTER must be set for the number of slave outdoor units that remain connected.

Operating outdoor unitsNumber of slavesSET3-3SET3-4
1 - Master only0OFFOFF
2 - Master + Slave 11OFFON
3 - Master + Slave 1 + Slave 22ONOFF
Master only number of slave unit setting
Master and one slave number of slave unit setting
Master and two slaves number of slave unit setting

4. Set the number of outdoor units - DIP SW SET5-1 and SET5-2

On the new MASTER, set DIP SW SET5-1 and SET5-2 to match the total number of outdoor units that are electrically connected and operating.

Number of outdoor unitsSET5-1SET5-2
1OFFOFF
2OFFON
3ONOFF
One outdoor unit SET5 setting
Two outdoor unit SET5 setting

When the third outdoor unit is returned to service, restore the three-outdoor-unit configuration and reset the switches accordingly.

Three outdoor units returned to service
Number of outdoor units DIP switch table

5. Final checks before operation

1Confirm the failed outdoor unit is electrically disconnected.
2Confirm the transmission wiring now terminates at the correct new MASTER outdoor unit.
3Confirm SET3-1 / SET3-2 address settings match the new master/slave arrangement.
4Confirm SET3-3 / SET3-4 match the number of slave units connected to the new master.
5Confirm SET5-1 / SET5-2 match the total number of operating outdoor units.
6Close the service valves on the non-operational outdoor unit.
Important: When the failed outdoor unit is repaired and returned to service, restore the original transmission wiring and outdoor-unit DIP switch configuration for the full system before commissioning the repaired configuration.
This procedure is based on the supplied VRF multi-outdoor-unit configuration information. Confirm the applicable model service documentation and current wiring diagram before changing transmission wiring or DIP switch settings.