Fujitsu FQ14 Repair Manual for Intermittent Power Failure

Safety First

Before you touch any part of your Fujitsu FQ14 air‑conditioner, ensure the unit is disconnected from all power sources. Turn off the main circuit breaker that supplies the unit and allow the compressor and fan motors to cool completely. Always work in a dry area and keep conductive tools away from electrical components. If you feel uncertain at any point, call a qualified HVAC technician.

Overview of the Problem

Intermittent power failures can manifest in several ways:

• The unit powers up, runs for a few minutes, then shuts off automatically.
• Power does not appear to be supplied to the compressor or fan.
• The indoor unit shows a flashing error LED or a “Power Failure” message on its display.
• The unit resets after a brief outage and resumes operation.

These symptoms often stem from loose connections, faulty control boards, or failing relays. Understanding the root cause is critical for a lasting repair.

Preliminary Checks

1. Visual Inspection

Open the access panels on both the indoor and outdoor units. Look for:

• Corroded or damaged wiring
• Disconnected or frayed power leads
• Signs of water ingress or condensation
• Damaged fuses or blown thermal overload relays

If you spot any obvious damage, repair or replace the affected part immediately.

2. Power Supply Verification

Using a multimeter, confirm that the mains voltage is present at the unit’s input terminals. A drop below 200 V (for a 220 V system) indicates a supply issue. If the mains supply is stable, proceed to component testing.

3. Capacitor Test

A faulty start capacitor can cause the compressor to stall intermittently. Measure the capacitor’s capacitance with a multimeter set to capacitance mode. If the reading is below the rated value by more than 10 %, replace the capacitor.

Diagnostic Checklist

Use this table to narrow down the most probable culprit before testing each component.

Component Testing

Power Relay

The power relay controls the flow of electricity to the compressor and fan. A relay that fails intermittently can lead to the symptoms described.

1. Locate the relay on the main board. It is usually a small rectangular component with several wires attached.
2. Remove the relay from its socket. Disconnect all wires.
3. Use a multimeter to check for continuity between the relay pins. A lack of continuity indicates a failed relay.
4. If the relay is defective, replace it with an identical part specified by Fujitsu for the FQ14 model.

Control Board

The control board orchestrates all functions. A malfunctioning board can misinterpret sensor data and cut power.

1. Inspect the board for burn marks, swollen electrolytic capacitors, or loose solder joints.
2. Test the board’s input and output pins using a multimeter. Each pin should show the expected voltage range as per the service manual.
3. If the board shows irregularities, replace it with a fresh board. Avoid re‑soldering if the board has multiple damaged components.

Thermal Overload Switch

This safety device trips when the compressor temperature exceeds safe limits.

1. Locate the thermal overload switch on the compressor bracket.
2. Press the reset button (if present). If the switch does not return to the “ON” position, it is faulty.
3. Replace the switch with a Fujitsu‑approved unit.

Wiring Harness

Intermittent power can be caused by a high‑resistance connection or a partially broken wire.

1. Measure resistance across each wire pair. The reading should be close to zero ohms. A high reading indicates a break or poor connection.
2. Inspect connectors for corrosion. Clean with isopropyl alcohol if necessary.
3. Replace any damaged wires or connectors.

Step‑by‑Step Repair Procedure

1. Disconnect Power

• Switch off the main breaker.
• Wait 30 seconds to ensure all capacitors have discharged.

2. Access the Indoor Unit

• Remove the front panel using the designated screws.
• Take note of how the panel is mounted to avoid misplacement.

3. Replace Faulty Relay

• Disconnect the relay from the board.
• Insert the new relay, ensuring each pin aligns correctly.
• Reconnect all wires.

4. Check the Control Board

• Inspect visually for damage.
• If replacing, align the new board with the mounting holes.
• Reconnect all peripheral wires.

5. Test the Thermal Overload

• Locate the switch, reset it, and confirm it holds the “ON” position.
• If it fails, swap in a new switch.

6. Inspect and Repair Wiring

• Measure each wire pair’s resistance.
• Replace any with high resistance or visible damage.
• Re‑solder or secure connectors as needed.

7. Re‑assemble the Unit

• Reinstall the front panel.
• Secure all screws.
• Ensure no tools or loose parts remain inside.

8. Reconnect Power

• Turn the main breaker back on.
• Wait a few seconds for the unit to initialize.

9. Verify Operation

• Observe the compressor and fan.
• Check for error LEDs or messages.
• If the unit runs continuously without shutting down, the repair is successful.

Final Checks

• Temperature Check: Allow the unit to run for 10 minutes. Verify that the indoor temperature stabilizes within the expected range.
• Noise Level: Listen for any abnormal sounds from the compressor or fan. A new relay should not produce clicking or buzzing.
• Electrical Load: Monitor the unit’s current draw using a clamp meter. It should stay within the rated range specified in the datasheet.

If any of these checks fail, revisit the corresponding component for additional troubleshooting.

Troubleshooting Recap

This table serves as a quick reference if you encounter the same issues again.

Maintenance Tips to Prevent Future Failures

• Regular Cleaning: Clean the outdoor condenser coils every 3 months to prevent overheating.
• Filter Replacement: Change the indoor air filter monthly during peak usage.
• Periodic Inspection: Check all wiring and connectors annually for corrosion or looseness.
• Run Cycle Checks: Let the unit run for at least 30 minutes once a month to ensure all components engage properly.
• Professional Service: Schedule a yearly inspection by a licensed HVAC technician.

Glossary of Key Terms

• Capacitor: An electronic component that stores electrical energy temporarily, aiding motor startup.
• Control Board: The central processor that controls fan speed, compressor timing, and sensor inputs.
• Thermal Overload Switch: A safety device that shuts off the compressor if temperatures rise beyond safe limits.
• Relay: An electrically operated switch that controls high‑current circuits using a low‑current signal.
• Coil: The heat exchanger in the outdoor unit that releases refrigerant heat to the environment.

With this guide, you should be able to diagnose and fix intermittent power failures in your Fujitsu FQ14 air conditioner confidently. Remember, safety first and keep a detailed record of all replacements and tests performed for future reference. Happy repairing!