Toshiba 1P55S2 Guide to Clear Fault 12 and Restore Performance

Introduction

The Toshiba 1P55S2 air conditioner is prized for its quiet operation and reliable performance. When an error appears on its display, it can feel like a sudden disruption in comfort. Fault 12 is one of the most common error codes and can appear for a variety of reasons—ranging from a simple sensor glitch to a deeper electrical or refrigerant issue. Understanding exactly what Fault 12 means, why it occurs, and how to correct it is essential for keeping the unit running smoothly.

This guide takes you through every step you need to clear Fault 12 and restore full performance. Whether you are a homeowner troubleshooting on your own or a technician preparing for a quick service visit, the instructions are clear, concise, and designed for practical application.

What Is Fault 12?

Fault 12 on a Toshiba 1P55S2 is an “Low Indoor Temperature Sensor Error.” The system’s internal controller monitors the indoor temperature sensor continuously. If the reading is significantly lower than expected or shows a sudden spike or drop, the controller flags Fault 12 and shuts the compressor to protect the unit.

Key points:

• The error is triggered by a faulty indoor temperature sensor, a damaged wiring connection, or a sensor miscalibration.
• It can also appear if the indoor unit’s evaporator coil becomes heavily iced, causing an abnormally low temperature reading.
• The display will show “Fault 12” and the LED indicator will flash.

Why Does Fault 12 Occur?

Before you dive into troubleshooting, it helps to know why the fault appears. Typical causes include:

1. Sensor Defect – Over time, sensors can degrade or become physically damaged, especially in humid or dusty environments.
2. Wiring Problems – Corrosion, loose connections, or short circuits between the sensor and the control board can cause incorrect readings.
3. Ice Formation – Excessive frost on the evaporator coil can make the sensor register a much lower temperature than actual.
4. Control Board Issues – In rare cases, the microcontroller on the indoor unit’s PCB can misinterpret signals.
5. Installation Problems – Incorrect sensor placement during installation can create a false low reading.

Understanding these causes gives you a roadmap for what to inspect and where to focus your attention.

Before You Start: Safety First

• Turn off Power: Disconnect the indoor unit’s power from the mains supply. Wait at least 30 seconds before touching any electrical components.
• Use a Multimeter: If you plan to test electrical continuity, set your meter to the appropriate voltage or continuity range.
• Wear Protective Gear: Safety glasses and gloves are recommended if you will be handling refrigerant lines or the unit’s cabinet.
• Know Your Warranty: If the unit is under warranty, contact Toshiba or an authorized dealer before opening the casing to avoid voiding coverage.

Step‑by‑Step Guide to Clear Fault 12

1. Verify the Error Code

1.1 Turn the indoor unit back on and watch the display for the “Fault 12” message.
1.2 Confirm the LED indicator is flashing; this ensures the fault is active and not a one‑time glitch.

2. Inspect the Indoor Temperature Sensor

2.1 Locate the sensor – it is usually mounted on the side of the indoor unit near the evaporator coil.
2.2 Check for visible signs of damage: cracks, discolouration, or corrosion.
2.3 Gently tap the sensor; a loose sensor may click back into place.

3. Test the Sensor’s Wiring

3.1 Open the indoor unit’s service panel (usually a small door on the back).
3.2 Verify that the sensor’s wires are securely fastened to the connector.
3.3 Look for frayed or burnt insulation.
3.4 Use a multimeter set to resistance to check continuity from the sensor to the connector. A reading of close to 0 Ω indicates a good connection.

4. Clean the Evaporator Coil

4.1 Dust and debris on the coil can promote ice build‑up.
4.2 Remove the front panel of the indoor unit.
4.3 Using a brush or compressed air (do not use water), clean the coil fins.
4.4 Check for visible frost; if present, allow the unit to run in “defrost” mode (often a switch on the remote) until the ice melts.

5. Replace the Sensor (If Needed)

5.1 If the sensor is damaged or the continuity test fails, order a replacement part from Toshiba or an authorized retailer.
5.2 Disconnect the old sensor’s connector.
5.3 Connect the new sensor, ensuring the pins line up correctly.
5.4 Tighten the connector securely.

6. Reset the Unit

6.1 With the power still disconnected, press and hold the power button on the indoor unit for 5 seconds.
6.2 Release the button, then restore power.
6.3 Observe the display; if the “Fault 12” message clears, the unit should resume normal operation.

7. Test Performance

7.1 Set the desired temperature on the remote.
7.2 Verify that the indoor unit lowers the room temperature steadily.
7.3 Check the fan speed and listen for unusual noises.

Verifying Performance After Fix

Once the fault is cleared, you want to be sure the unit is running at full capacity.

• Temperature Readings: Use a separate thermometer to confirm the room temperature matches the remote setting.
• Compressor Operation: The compressor should cycle on and off at appropriate intervals. If it runs continuously, the system may be over‑cooling.
• Noise Levels: Quiet operation indicates the motor and fan are functioning correctly.
• Power Consumption: Monitor the electric bill or use a plug‑in meter to ensure the unit’s energy draw is within normal limits.

If any of these checks reveal issues, consider a deeper inspection of the compressor or refrigerant charge.

Common Mistakes to Avoid

Maintenance Tips to Prevent Future Fault 12

• Monthly Coil Cleaning: Dust accumulation is a frequent cause of sensor‑related errors.
• Quarterly Professional Service: A technician can check refrigerant levels and sensor calibration.
• Keep the Outdoor Unit Unobstructed: Adequate airflow reduces compressor load and sensor strain.
• Monitor Indoor Humidity: High humidity can promote ice on the coil; consider a dehumidifier in very damp environments.
• Update Firmware: If your Toshiba unit supports remote firmware updates, ensure it runs the latest version; sometimes software bugs trigger erroneous fault codes.

Frequently Asked Questions

1. Can Fault 12 be a false alarm?

Yes. If the indoor temperature sensor is positioned too close to a heat source or the wiring has a minor crack, the sensor may temporarily register a lower temperature and trigger the fault. Replacing the sensor or adjusting its position often resolves the issue.

2. How long does a sensor replacement take?

A trained technician can replace the sensor in about 10 minutes. If you are comfortable with basic electrical work, the process takes around 20 minutes.

3. Will clearing Fault 12 affect the warranty?

Only if you open the unit’s casing yourself. Authorized service personnel will not void the warranty. If your unit is still under warranty, contact Toshiba or a certified dealer for service.

4. What if the fault reappears after replacement?

Re‑check the wiring and ensure there is no damage on the new sensor’s leads. Verify that the sensor is not installed upside down. If the fault persists, the control board may be defective and needs inspection by a professional.

5. Is there a risk of refrigerant loss after cleaning the coil?

No. Coil cleaning does not affect the refrigerant charge. However, if you notice a sudden drop in cooling performance after cleaning, schedule a service visit to verify the refrigerant level.

Conclusion

Fault 12 on a Toshiba 1P55S2 is a straightforward error that signals a problem with the indoor temperature sensor or its connections. By following the step‑by‑step guide above—verifying the fault, inspecting and testing the sensor, cleaning the coil, replacing the sensor if necessary, and resetting the unit—you can clear the error and restore the air conditioner’s performance.

Regular maintenance, including monthly coil cleaning and quarterly professional checks, will reduce the likelihood of future faults. Armed with these practices, you’ll keep your home cool and comfortable all year long.