General Assist Technical Reference
Controller PCB Checks
Controller functions, connector identification and expected supply voltages
Use this reference when checking the outdoor unit Controller PCB and connected components.
The Controller PCB performs the main control calculations for the system and manages protection, compressor speed, fan operation, expansion valve control, sensor inputs, defrost and reversing valve operation.
Electrical safety: These checks include approximately 240 V AC and 330–370 V DC. High DC voltage may remain present after power is isolated. Testing must only be completed by suitably qualified personnel using appropriate test equipment and safe electrical work practices.
1. Controller PCB functions
| Function | Controller responsibility |
|---|---|
| Control calculations | Main operating calculations are performed by the Controller PCB. |
| Protection and safety | Monitors and controls system protection and safety functions. |
| Compressor | Controls compressor speed. |
| Outdoor fan motor | Controls fan motor operation. |
| Electronic Expansion Valve | Controls the EEV coil. |
| Thermistors | Receives temperature sensor inputs. |
| Pressure transducer | Receives pressure sensor input. |
| Defrost | Controls defrost operation. |
| Reversing / 4-way valve | Controls reversing valve operation. |
2. Main Controller PCB connections
| Connection / component | Reference from training material |
|---|---|
| Control harnesses | Harnesses connect to the TR PCB, ACTPM and Filter PCB. |
| Outdoor fan motor plugs | Fan motor power and low-voltage control supply connections. |
| DC fuse | Replaceable 3.15 A DC fuse. |
| Main PCB DC power input | High-voltage DC supply to the Controller PCB. |
| Indoor-unit communication | Signal chip provides communication to the indoor unit. |
| AC power input | AC supply into the Controller PCB. |
| Electronic Expansion Valve | EEV coil connection. |
| High pressure sensor | Pressure transducer / sensor connection. |
| Thermistors | Temperature sensor connections. |
| Reversing valve solenoid | Energised in HEAT mode. |
3. Expected voltages
Use the values below as the expected references shown in the Controller PCB training material. Connector identification and exact test points must be confirmed against the applicable model service information before testing.
| Circuit / component | Expected supply | Notes |
|---|---|---|
| Main PCB DC power input | 330–370 V DC | High-voltage DC supply into the Controller PCB. |
| Outdoor fan motor — Red to Black | 330–370 V DC | High-voltage fan motor supply. |
| Outdoor fan motor — White to Black | 15 V DC | Low-voltage fan motor supply reference. |
| Electronic Expansion Valve coil | 12 V DC | EEV control supply. |
| High pressure sensor | 5 V DC | Sensor supply. |
| Thermistors | 5 V DC | Temperature sensor circuit reference. |
| Reversing valve solenoid | 240 V AC | Energised in HEAT mode. |
| Controller PCB AC power input | 240 V AC | AC supply into the PCB. |
4. Controller PCB check sequence
- Visually inspect the PCB and harnesses. Check plugs are fully seated and look for obvious heat damage, contamination or damaged wiring.
- Check the replaceable 3.15 A DC fuse. If the fuse has opened, determine the cause before replacement.
- Confirm PCB power supplies. Check for the expected 240 V AC input and 330–370 V DC main PCB supply using the applicable model service information.
- Check the outdoor fan motor supplies. The source identifies 330–370 V DC from Red to Black and 15 V DC from White to Black.
- Check low-voltage component supplies. The EEV circuit is referenced at 12 V DC, while the high-pressure sensor and thermistor circuits are referenced at 5 V DC.
- Check reversing valve output when applicable. The reversing valve solenoid is identified as a 240 V AC output energised in HEAT mode.
- Confirm communication and control harnesses. Inspect the communication section to the indoor unit and the harnesses to the TR PCB, ACTPM and Filter PCB.
Important: An abnormal voltage does not automatically confirm a failed Controller PCB. The connected load, upstream power circuitry, harness condition and applicable model-specific service information must also be checked before condemning the PCB.
5. Quick reference
| 330–370 V DC | 15 V DC | 12 V DC | 5 V DC | 240 V AC |
|---|---|---|---|---|
| Main PCB DC input Fan Red–Black | Fan White–Black | EEV coil | High-pressure sensor Thermistors | PCB AC input Reversing valve in HEAT |
Technical reference prepared from the supplied Controller PCB training material. Always refer to the applicable model service manual and wiring diagram for connector locations and model-specific diagnostic procedures.