Summary

This article outlines a safe, repeatable method to diagnose EEV faults. There are three potential failure points: coil, controller PCB supply, and mechanical valve body. The steps below show how to confirm or eliminate each one.

Applies to

  • Split and VRF systems using 5-wire or 6-wire EEV coils

  • Service and commissioning technicians performing on-site diagnostics

Background (how the EEV behaves)

  • Function: The EEV regulates refrigerant flow to the indoor coil using pipe-temperature feedback. Faulty thermistors can therefore affect EEV behaviour.

  • Positions: With no power, the valve opens to allow pressure equalisation and evacuation. When powered, the coil first drives the valve closed and it re-opens per control demand.

Safety

  • Isolate mains before unplugging any connectors.

  • Use DC ranges for PCB supply checks; avoid shorting adjacent pins.

  • Keep hands/tools clear of moving parts when power is restored.

Overview of tests

  1. Coil resistance — validates the coil windings.

  2. PCB DC supply — confirms the outdoor PCB is providing correct voltage.

  3. Mechanical movement — verifies the valve body isn’t stuck.

Step 1 — Coil resistance test (Power OFF)

Identify coil type, then measure resistance at ~20 °C.

  • For 5-wire coils, use red as the active reference.

  • For 6-wire coils, red is the active for white/orange and brown is the active for blue/yellow.

Expected resistance (at ~20 °C):

  • 12 V DC coils: 42–50 Ω

  • 24 V DC coils: 183–191 Ω

Measure across:

  • Red ↔ White

  • Red ↔ Orange

  • Red (5-wire) or Brown (6-wire) ↔ Blue

  • Red (5-wire) or Brown (6-wire) ↔ Yellow

Pass/Fail:

  • Pass: All pairs within the specified band.

  • Fail: Any open/short or out-of-range value → replace the EEV coil.

Step 2 — PCB DC supply test (Power ON)

2A) Quick sound check

After restoring power from an isolated state, listen for four ticks as the coil re-indexes at start-up. Absence of ticks warrants a voltage test.

2B) Voltage measurement at the outdoor PCB

  1. Unplug the EEV coil. If the outdoor fan motor is DC, unplug it to access a reliable DC neutral (the black fan lead) on the PCB. Note the pin positions before testing.

  2. Place the black probe on the fan motor’s black (DC neutral) pin.

  3. Place the red probe on:

    • Red pin (EEV coil) — 12 V supply (both 5- and 6-wire coils).

    • Brown pin (6-wire only) — second 12 V supply line.

  4. Confirm a stable ~12 V DC on the relevant pin(s). Probing can be done from the rear of the plugs if tips are thin enough.

Pass/Fail:

  • Pass: Correct DC present on required pin(s).

  • Fail: Missing/unstable DC → suspect outdoor PCB (after confirming harness and connectors).

Step 3 — Mechanical movement check (Power OFF)

If the coil and PCB tests pass but performance is abnormal:

  1. Remove the coil from the valve body.

  2. Using a magnet, gently rotate the valve core clockwise to open and anti-clockwise to close.

  3. Refit the coil, power the system, and check for a temperature differential across the valve body.

  4. Fail: No response or no temperature change → replace the valve body.

Result interpretation — quick reference

  • Open/short coil or out-of-spec resistance → Replace coil.

  • No DC at PCB pins (with correct probing) → Investigate/replace outdoor PCB.

  • Electrical tests pass, no movement/ΔT → Replace valve body.

Notes & tips

  • If EEV behaviour seems erratic with sound electrical checks, verify pipe thermistors—EEV control is thermistor-driven.

  • The EEV opens when de-energised; leverage this for evacuation and pressure equalisation during service.