General Assist Technical Reference
LATT 3 Phase Controller PCB
Power input, DC conversion, test points, fuses and controller functions
Technical reference for LATT 3 phase outdoor controller PCB diagnostics
The LATT 3 phase outdoor controller PCB receives the incoming AC supply, monitors phase rotation, converts the supply to a high-voltage DC bus, and generates the low-voltage DC supplies used by the outdoor unit control circuits.
Electrical safety: The controller PCB contains hazardous mains and high-voltage DC. Testing must only be carried out by appropriately qualified personnel using suitable test equipment and safe electrical work procedures.
1. Controller PCB overview
| Function | Controller PCB role |
|---|---|
| AC power input | Receives the outdoor-unit AC supply through connector CN101. |
| Phase rotation protection | Uses the L2, L3 and neutral inputs for phase-rotation monitoring. |
| AC to DC conversion | The diode bridge converts the 240 V AC supply to approximately 330–370 V DC. |
| Low-voltage generation | A DC transformer provides 5 V, 12 V and 15 V DC control supplies. |
| System status | On-board display LEDs provide system status and are used for Test Run and Pump Down functions. |
2. Power supply input – CN101
The source material identifies CN101 as the controller PCB power-supply input.
| Wire colour | Connection | Purpose |
|---|---|---|
| Blue | N | Neutral input |
| White | L2 | AC supply / phase-rotation monitoring |
| Black | L3 | AC supply / phase-rotation monitoring |
Important: The controller PCB AC input uses L2, L3 and N as shown in the source material. These inputs are also used for phase-rotation protection.
3. Diode bridge and DC bus
The diode bridge is located on the controller PCB and converts the incoming 240 V AC supply to a high-voltage DC supply.
| Test / component | Source reference |
|---|---|
| Diode bridge output | Approximately 330–370 V DC |
| DC test point | Located at the top-left corner of the controller PCB |
| Test ground | Pin 102 can be used as ground when testing components |
High-voltage DC: A reading of 330–370 V DC is hazardous and can remain present after the supply is removed. Follow the applicable discharge and verification procedure before touching the PCB or connected components.
4. Controller PCB fuses
| Fuse rating | Protected circuit |
|---|---|
| 10 A | Power supply to the indoor unit |
| 3.15 A | Power supply for serial communication |
| 5 A | Power supply for DC circuits |
5. DC supplies and controller functions
The controller PCB generates its own DC supplies for both high-voltage and low-voltage circuits.
| Circuit / output | Function |
|---|---|
| 330–370 V DC | High-voltage DC supply used for the outdoor fan motors |
| 5 V / 12 V / 15 V DC | Low-voltage control supplies generated through the DC transformer |
| Low-voltage circuits | Used by EEV control, pressure sensors and thermistors |
| Display LEDs | Display system status and support Test Run and Pump Down functions |
6. Technician test reference
| 1 | Confirm CN101 supply connections: Blue = N, White = L2, Black = L3. |
| 2 | Check the high-voltage DC bus: The controller PCB DC test point is located at the top-left corner. Expected source reference: 330–370 V DC. |
| 3 | Use Pin 102 as ground when testing the relevant controller PCB components, as identified in the source material. |
| 4 | Inspect the protection fuses: 10 A indoor-unit supply, 3.15 A serial communication supply and 5 A DC-circuit supply. |
| 5 | Confirm low-voltage control supply availability where applicable: 5 V, 12 V and 15 V DC circuits are generated by the controller PCB DC transformer. |
| 6 | Review the display LEDs for system status and when carrying out Test Run or Pump Down functions. |
Key reference: The LATT 3 phase controller PCB performs more than basic logic control. It also receives the AC supply, provides phase-rotation protection, rectifies the supply to 330–370 V DC, produces the 5 V / 12 V / 15 V DC control supplies, and distributes protected power to key circuits.
General Assist technical reference. Use the applicable service documentation and electrical safety procedures when carrying out testing or repairs.