Fujitsu FQ-13B Repair Steps for Failure to Turn On

Safety Precautions

Before you begin any work on your Fujitsu FQ‑13B air conditioner, make sure you understand the basic safety rules that apply to all electrical appliances. Failure to follow these steps can cause injury or permanent damage to the unit.

• Disconnect the power: The most important rule is to cut off the power supply. Locate the main circuit breaker that feeds the HVAC circuit and switch it off. If the unit is powered from a dedicated 240‑volt split‑phase circuit, turn off the breaker that corresponds to that circuit.
• Verify zero voltage: After the breaker is off, use a voltage tester or a multimeter set to AC volts to confirm that the terminals at the unit’s indoor or outdoor fan motor are truly at zero volts. Touch the tester leads to the terminals; if the display reads any voltage, restore power before proceeding.
• Avoid water contact: The FQ‑13B is a wet‑environment appliance. Keep all tools and your hands dry.
• Wear protective gear: A pair of insulated gloves and safety glasses can help prevent accidental shocks or injury.
• Do not work alone: If possible, have another person present. One can handle tools and power disconnects while the other works on the unit.

Skipping these precautions is not a minor oversight—it can result in serious injury or even death.

Overview of the FQ‑13B

The Fujitsu FQ‑13B is a split‑supply air‑conditioning system that is commonly used in residential and light commercial settings. The indoor unit is a low‑voltage wall‑mounted fin‑coil, while the outdoor condenser contains the compressor, high‑pressure line, and fan. Because the unit operates on 240 V, a failure to turn on can arise from many different causes: power supply problems, thermostat malfunction, relay failure, or a bad fan motor.

When troubleshooting a unit that does not power on, follow a systematic approach. First, rule out simple electrical issues—breaker, fuses, and the main power supply. Next, check the thermostat and control board. Finally, test the components that drive the compressor and fans. By working through the system in order of “importance,” you minimize the risk of opening the wrong part and missing the root cause.

Diagnostic Checklist

Before you dive into disassembly, go through this quick checklist. Each item will give you a hint about where to focus your investigation.

If any of the above items reveals a problem, address it before moving on. If all of them appear normal, it’s time to open the panels and investigate deeper.

Step‑by‑Step Repair

Below is a comprehensive step‑by‑step guide to diagnosing and fixing a Fujitsu FQ‑13B that refuses to turn on. The instructions assume you have a working multimeter and basic hand tools (screwdrivers, pliers). If you are unsure about any step, consult a professional HVAC technician.

1. Re‑Check Power Delivery

1. Turn on the breaker: After verifying that the breaker is not tripped, switch it back on.
2. Use a voltage tester: With the power back on, test the supply terminals at the indoor unit. You should read ~240 V AC between the L1 and L2 conductors and ~120 V AC between each live and neutral.
3. Verify continuity: If any of these readings are missing or low, trace the wiring back to the breaker panel. Look for loose connections, burnt wires, or a faulty circuit breaker.

If power is confirmed, proceed to the next step. If not, replace any damaged wiring or breakers.

2. Inspect the Thermostat

1. Open the thermostat housing: Remove the cover and check for any visible scorch marks or loose wiring.
2. Test the thermostat’s internal relay: Using a multimeter on the continuity setting, confirm that the thermostat’s switch engages when the set temperature is exceeded.
3. Reset or replace: If the thermostat is unresponsive, replace it with a new unit of the same model. Ensure that the new thermostat’s wiring matches the old one exactly.

A faulty thermostat is the most common reason an air conditioner will not turn on.

3. Examine the Indoor Control Board

The indoor unit houses a small printed circuit board (PCB) that controls fan speed, compressor start, and error diagnostics.

1. Open the indoor cabinet: Remove the panel screws and lift the cover carefully.
2. Look for visible damage: Burn marks, cracked solder joints, or blown capacitors are obvious signs of failure.
3. Test the main control relay: The relay is usually a small rectangular component with two or three pins. Use a multimeter set to resistance and place one probe on each pin. A healthy relay should show a resistance of 0–5 Ω when energized and open (infinite resistance) when de‑energized.
4. Swap if necessary: If the relay fails the test, replace it with a compatible part (usually 24 VDC, 10 A).

If the PCB appears fine but the unit still won’t start, move on to the compressor.

4. Check the Compressor Start Relay and Capacitor

The outdoor unit contains a relay that triggers the compressor and a start capacitor that gives the compressor the extra torque to start.

1. Locate the compressor relay: It is a square component on the main board with a large terminal.
2. Test the relay: Use the same resistance test as in step 3.
3. Inspect the start capacitor: It is a small cylindrical part attached to the compressor.
   • Visual inspection: Look for bulging, leakage, or corrosion.
   • Capacitance test: With the unit off, set the multimeter to the capacitance setting and touch the probes to the capacitor leads. The reading should be within ±10 % of the capacitor’s rated value (usually 0.1–1 µF).
4. Replace if needed: If the capacitor is low or open, swap it for a new unit. If the relay is stuck, replace it.

An exhausted capacitor or relay is a common cause of a “no start” condition.

5. Verify the Outdoor Fan Motor

The outdoor unit’s fan is critical for cooling the condenser coils. A failed fan will prevent the compressor from getting enough cooling air.

1. Listen for the fan: When you turn on the power, the fan should start immediately.
2. Test the fan motor: Remove the fan pulley cover. Use a multimeter on the resistance setting and touch the leads to the motor’s terminals. A working motor should show a reading around 0.5–1.5 Ω.
3. Check for mechanical obstructions: Rotate the fan blades manually. They should spin freely. If they feel stiff, the bearings may have failed.
4. Replace or lubricate: If the motor is dead, replace it. If the bearings are worn, replace the motor or install a fan bearing grease kit.

A defective fan is a quick win; often replacing it solves the problem.

6. Inspect the High‑Pressure Line and Pressure Switch

The high‑pressure line connects the outdoor unit to the indoor coil. A blockage can cause the compressor to fail to start.

1. Check the line for kinks or obstructions: Ensure the line is not pinched or crushed.
2. Test the pressure switch: The switch is usually located on the compressor housing. Use a multimeter on the continuity setting while pulling the switch lever. It should have continuity only when the lever is engaged.
3. Replace if faulty: If the switch fails, replace it.

This step is optional if the unit has no error code indicating high pressure, but it is a useful check if previous steps did not reveal a problem.

7. Confirm the Power Supply to the Compressor

Sometimes the compressor’s own power leads may have failed.

1. Locate the compressor’s power terminals: These are usually labeled L1, L2, and N.
2. Test for voltage: With the unit powered on, use a multimeter to confirm ~240 V between L1 and L2, and ~120 V between L1 and N (or L2 and N).
3. Check for continuity: With power off, test the continuity between each terminal and the compressor’s housing. A broken conductor will show open circuit.

If you find any open or intermittent connection, repair the wiring or replace the faulty cable.

8. Re‑assemble and Test

After you have replaced any faulty components, reassemble the unit in reverse order of disassembly.

1. Re‑install the panels: Make sure all screws are tightened but not overtightened.
2. Restore power: Switch the breaker back on.
3. Set the thermostat: Set it above the room temperature.
4. Observe the sequence: The indoor fan should spin, the indoor display should show a status, and the outdoor fan should start.
5. Check for error codes: If any codes appear, refer to Fujitsu’s troubleshooting guide.

If the unit starts and runs, congratulations! If not, review the steps again; a small component might have been missed.

Common Pitfalls and How to Avoid Them

When to Call a Professional

Even if you can replace most parts yourself, certain situations warrant a licensed HVAC technician:

• High‑voltage work: If you are uncomfortable dealing with 240 V circuits.
• Complex electrical failures: For instance, a damaged main board that requires soldering.
• Compressor issues: Replacing a compressor is often costly and may require refrigerant recovery.
• Refrigerant handling: If the system has low refrigerant or a leak, only a certified technician should recover and recharge the charge.

When in doubt, call a professional. An improper repair can lead to larger damage or safety hazards.

Quick Reference Summary

• Power: Verify breaker, voltage, and wiring.
• Thermostat: Check relay and replace if needed.
• Indoor board: Inspect for damage; test relay.
• Compressor start: Test relay and capacitor.
• Outdoor fan: Listen, test resistance, and replace motor if necessary.
• High‑pressure line: Ensure no blockage; test pressure switch.
• Compressor power: Check voltage and continuity.
• Re‑assemble carefully and test the system.

By following this structured approach, you can pinpoint the cause of a Fujitsu FQ‑13B that won’t turn on and address it efficiently. A methodical diagnosis saves time, money, and reduces the risk of future failures.