General Assist Technical Reference
Outdoor Filter PCB Check
Filter PCB function, voltage checks and component inspection
Technical reference for checking the outdoor unit Filter PCB
The outdoor Filter PCB provides electrical filtering and protection functions and also distributes AC power to downstream circuits. When diagnosing the board, check the incoming supply, outgoing AC supplies, fuses and visible protective components.
1. Filter PCB Function
The Filter PCB contains a number of protective and filtering components used by the outdoor unit.
| Component / Function | Purpose |
|---|---|
| Varistors / Surge Absorbers | Protect downstream circuits from electrical surges. |
| Copper Electrical Noise Filters | Reduce and filter electrical interference. |
| Current Transformer (CT) | Monitors outdoor unit operating current so compressor speed can be adjusted accordingly. |
| Fuses | Provide circuit protection. On some models the fuses are hardwired to the PCB. |
| PTC Thermistor Connection | Connection from the Filter PCB to the PTC thermistor circuit. |
Varistor inspection
Varistors are sacrificial protective components. When subjected to a damaging surge they can create a short between Active and Neutral. A failed varistor will commonly show visible signs of damage or burning.
2. Voltage Checks
The reference identifies three key AC voltage checks on the Filter PCB.
| Check Point | Expected Voltage | Purpose |
|---|---|---|
| Mains AC IN | ~ AC 230 V | Confirms mains supply is reaching the Filter PCB. |
| AC Supply to Indoor Terminals IN | ~ AC 230 V | Confirms the Filter PCB is supplying AC power towards the indoor terminal circuit. |
| AC Supply to Diode Bridge IN | ~ AC 230 V | Confirms AC power is leaving the Filter PCB and reaching the diode bridge input. |
Key diagnostic principle: If approximately 230 VAC is present at Mains AC IN but is missing at one of the Filter PCB outputs, investigate the Filter PCB, its fuse protection and associated connections.
3. Component Checks
Fuses
Inspect and electrically test the Filter PCB fuses.
Important: On some outdoor unit models the fuses are hardwired to the Filter PCB. If a hardwired fuse is open, the complete Filter PCB may require replacement.
Varistors
- Inspect for burning, cracking, discolouration or other visible damage.
- Damage can indicate that the varistor has operated in response to an electrical surge.
- A failed varistor may create a short between Active and Neutral.
Noise Filter Coils
The large copper-wound components on the Filter PCB are electrical noise filters used to reduce electrical interference.
Inspect these components and their soldered connections for obvious physical or heat damage.
Current Transformer
The Current Transformer (CT) monitors the operating current of the outdoor unit. This information is used by the control system when adjusting compressor speed.
PTC Thermistor Connection
Check the connection from the Filter PCB to the PTC thermistor and confirm the connector and wiring are secure and undamaged.
4. Diagnostic Sequence
| 1 | Confirm approximately 230 VAC is present at the Mains AC IN connection. |
| 2 | Inspect the Filter PCB for obvious signs of burning, damaged varistors, damaged components or heat-affected connections. |
| 3 | Check the Filter PCB fuses for continuity. |
| 4 | Confirm approximately 230 VAC at the AC supply to Indoor Terminals IN. |
| 5 | Confirm approximately 230 VAC at the AC supply to Diode Bridge IN. |
| 6 | Inspect the PTC thermistor connection, Current Transformer and associated wiring. |
5. Quick Reference
| Item | Check |
|---|---|
| Mains AC IN | Approximately 230 VAC |
| Indoor Terminal Supply | Approximately 230 VAC |
| Diode Bridge Input | Approximately 230 VAC |
| Varistors | Check for visible damage or burning |
| Fuses | Check continuity |
| CT | Check wiring and connection |
| PTC Thermistor | Check connector and wiring |
Electrical safety: These checks involve live mains voltage. Testing should only be carried out by appropriately qualified personnel using suitable test equipment and safe electrical work practices.