General Assist Technical Reference
EEV Diagnostic Testing
Coil resistance, PCB DC supply and mechanical valve-body checks
For split and VRF systems using 5-wire or 6-wire electronic expansion valve (EEV) coils
Purpose: Use this procedure to determine whether an EEV fault is caused by the coil, the outdoor controller PCB supply, or the mechanical valve body.
Safety: Isolate mains power before unplugging connectors or removing the EEV coil. Restore power only when instructed for live DC checks. Use the DC range on the meter and avoid shorting adjacent PCB pins.
1. How the EEV operates
- Function: The EEV regulates refrigerant flow to the indoor coil using pipe-temperature feedback. Incorrect thermistor readings can therefore affect EEV operation.
- De-energised: With no power, the valve opens to assist pressure equalisation and evacuation.
- Powered: At start-up, the coil first drives the valve closed, then re-opens according to control demand.
Diagnostic sequence: Test the coil first, then confirm PCB supply voltage, then check mechanical movement only if the electrical checks pass.
2. Step 1 - Coil resistance test (Power OFF)
Identify the coil type and measure winding resistance at approximately 20°C.
Reference wiring:
5-wire coil: Red is the active reference.
6-wire coil: Red is the active reference for White/Orange, and Brown is the active reference for Blue/Yellow.
5-wire coil: Red is the active reference.
6-wire coil: Red is the active reference for White/Orange, and Brown is the active reference for Blue/Yellow.
| Coil Type | Expected Resistance at ~20°C |
|---|---|
| 12 V DC coil | 42-50 Ω |
| 24 V DC coil | 183-191 Ω |
Measurement pairs
| Measurement | Applicable Coil |
|---|---|
| Red ↔ White | 5-wire and 6-wire |
| Red ↔ Orange | 5-wire and 6-wire |
| Red ↔ Blue | 5-wire |
| Red ↔ Yellow | 5-wire |
| Brown ↔ Blue | 6-wire |
| Brown ↔ Yellow | 6-wire |
Pass: All required winding pairs are within the specified resistance range.
Fail: Any winding is open-circuit, short-circuit or outside specification - replace the EEV coil.
3. Step 2 - PCB DC supply test (Power ON)
A. Quick start-up sound check
After restoring power from an isolated state, listen for approximately four ticks as the EEV re-indexes at start-up. If no ticks are heard, continue with the voltage test.
B. Voltage measurement at the outdoor PCB
- Isolate power and unplug the EEV coil.
- If the outdoor fan motor is DC, unplug it as required to access the black fan-motor lead/pin, which is used as the DC neutral reference. Record the pin positions before testing.
- Restore power and set the multimeter to V DC.
- Place the black meter probe on the fan motor's black DC-neutral pin.
- Place the red meter probeon the EEV supply pin(s):
- Red pin: approximately 12 V DC supply on both 5-wire and 6-wire coils.
- Brown pin: approximately 12 V DC second supply line on 6-wire coils only.
- Confirm a stable ~12 V DC on the required pin(s). Where practical, probing may be carried out from the rear of the connector with suitable fine probes.
Pass: Correct DC voltage is present on the required EEV supply pin(s).
Fail: Missing or unstable DC supply - inspect the harness and connectors first. If wiring is sound, suspect the outdoor controller PCB.
4. Step 3 - Mechanical movement check (Power OFF)
Use this check only when the coil resistance and PCB supply tests have passed but system performance remains abnormal.
- Isolate power and remove the EEV coil from the valve body.
- Using a suitable magnet, gently rotate the valve core:
- Clockwise: open
- Anti-clockwise: close
- Refit the coil, restore power and operate the system.
- Check for a temperature differential (ΔT) across the valve body to confirm refrigerant-flow response.
Fail: If there is no mechanical response or no temperature change after the electrical checks have passed, replace the valve body.
5. Result interpretation - quick reference
| Test Result | Likely Fault | Action |
|---|---|---|
| Open/short winding or resistance outside specification | EEV coil | Replace coil |
| Required DC supply missing or unstable | Harness / outdoor PCB | Check wiring/connectors, then investigate PCB |
| Electrical checks pass but valve does not move / no ΔT | Mechanical valve body | Replace valve body |
6. Notes and troubleshooting tips
- If EEV behaviour is erratic but the electrical checks are normal, verify the associated pipe thermistors. EEV control relies on thermistor feedback.
- The EEV opens when de-energised. This can assist pressure equalisation and evacuation during service.
- Always confirm connector condition and wiring continuity before condemning an outdoor PCB.
Technical information should be used in conjunction with the applicable service documentation for the specific model being tested.