This details the the communication checks for the R410a Units. This is not for R32 models. Be sure to verify what you have before testing.

 

Fujitsu H-Series Communication Error Troubleshooting Guide (R410A Units)

Note: This guide applies specifically to Fujitsu H-Series R410A multi-split and single-zone systems. It does not apply to R32 models.

Required Tools & Prerequisites

• Digital Multimeter: Must read up to at least 20 MΩ and be equipped with needle-point leads (standard blunt leads will not make proper contact).

• Pre-Check System Behavior:

   

  • If all indoor heads show a communication error, prioritize troubleshooting the outdoor unit.

  • If only one head shows an error, isolate that specific head, line set, and connection terminal.

Phase 1: Installation & External Diagnostics

Before condemning boards or components, check for external communication disruptions:

 

1. Wired Wi-Fi Modules: If a wired Wi-Fi adapter is installed without an active Wi-Fi connection, it may trip a false communication fault.

2. Condensate Safety Switches: Verify that inline condensate overflow switches have not broken circuit continuity.

3. Disconnect Switches: Check 3-pole disconnects for loose lugs or voltage drops across contacts.

4. Wiring Integrity: Ensure continuous, unbroken wire runs. Wire nuts are strictly prohibited on communication circuits. Verify tight terminal block connections and solid earth ground.

Phase 2: Communication Signal Voltage Testing

High-Voltage Safety Warning

Turn off all power disconnects before removing wires or board covers. Restore power only when ready to measure live operating voltages.

 

1. Power down the system.

2. Disconnect wire #3 at the outdoor unit (or indoor unit).

3. Restore power and take the following measurements:

• Line Voltage: Measure across L1–L2 and outdoor terminals 1–2 to confirm incoming 208/230 VAC.

• Outdoor Signal Output: Measure DC voltage from Terminal #3 to Ground.

   

  • Normal Reading: A pulsing 50–170 VDC (fluctuating by at least 20V).

  • Fault Condition: A steady/flat DC voltage (typically around ~56 VDC) indicates a defective outdoor communication circuit.

• Indoor Signal Output: Measure DC voltage from the disconnected #3 wire to Ground.

   

  • Normal Reading: Should read > 100 VDC (or a fluctuating 70–100 VDC signal returning from the indoor head).

Phase 3: Outdoor Board & Inverter Checks (ACTPM & Solder Points)

If the communication signal is absent or flat, check the DC bus and power supply delivery to the inverter assembly:

 

1. ACTPM (Active Filter Module) DC Readings:

    

   • Black to Red: Must read a DC voltage higher than incoming AC line voltage (L1–L2).

   • Yellow to Blue: Must read a DC voltage at least 30 VDC higher than the Black-to-Red reading.

   • White to Brown: Must read 0 VAC.

2. Board Solder Points & Connector Power:

    

   • Measure AC voltage across solder joints W10 and W11: Must read line voltage (~208/230 VAC).

   • Locate CN34 solder points on the inverter board: Must read line voltage (~208/230 VAC).

Phase 4: Mandatory Component Testing Before Board Replacement

Component Failure Risk

Never replace a failed control board without thoroughly testing the EEV coils, fan motor(s), and compressor. A shorted motor or valve will immediately destroy a new replacement board.

 

1. Electronic Expansion Valve (EEV) Coils

Disconnect the EEV connector and measure winding resistances across the designated pin pairs:

 

• 5-Wire & 6-Wire Coils: Test White–Red, Yellow–Red/Brown, Orange–Red, Blue–Red/Brown.

• Expected Resistance: 46 Ω ± 4 Ω at 68°F (20°C).

• If resistance is open or out of spec, replace the EEV coil.

2. DC Fan Motor Resistance Checks

Disconnect the fan motor plug from the board and measure from each color lead to Black (Ground/Common): Each Model Is Different See Link Outdoor Fan Motor Check

 

Motor Model	Red – Black	White – Black	Yellow – Black	Brown / Blue – Black
MFE-60TVT	300 kΩ – OL	45 kΩ – 55 kΩ	120 kΩ – 140 kΩ	Megaohms – OL
MFE-45WVT / MFE-45ROM	300 kΩ – OL	40 kΩ – 100 kΩ	120 kΩ – 140 kΩ (or up to 210 kΩ)	Megaohms – OL

3. Inverter Compressor Resistance & Insulation

• Phase-to-Phase: Measure across all three terminals (U-V, V-W, W-U). Resistance should be balanced and identical across all windings (typically ~1 Ω).

• Phase-to-Ground: Measure from each terminal to bare copper ground. Any reading ≤ 10 MΩ indicates a grounded compressor and requires replacement.

Best Practice Rule

Whenever replacing a damaged outdoor control board, always replace the Active Filter Module (ACTPM) at the same time to absorb electrical spikes and prevent repeat failures.