How to Fix P8 Error Code on a Mitsubishi Air Conditioner

The P8 error code on a Mitsubishi Mr. Slim air conditioning unit generally indicates an issue with the outdoor condenser unit. This problem can arise due to multiple reasons, such as wiring issues, sensor malfunctions, or faults in the outdoor unit’s components. Below are the common causes and their respective solutions:

1. Compressor Command Phase Detected (LED 1 Flashing)

• Cause: This issue may occur when the compressor detects an incorrect phase due to improper installation or wiring issues, especially in a three-phase electrical setup.
• Solution: Rewiring the outdoor unit’s motor correctly may resolve the error. Ensure that all connections are secure. If you are not experienced with electrical work, it is recommended to hire a professional technician.

2. Operation Sensor Short or Open (LED 3 Flashing)

• Cause: This error may indicate a high-pressure safety issue, often resulting from a bad fan motor or a corroded refrigeration circuit.
• Solution: Troubleshoot the outdoor unit and, if needed, replace the faulty fan motor or address any issues with the refrigeration circuit.

3. 4-Way Valve On Switch 26C (LED 6 Flashing)

• Cause: This issue might be caused by a faulty discharge thermistor, low refrigerant levels, or other related problems.
• Solution: Troubleshoot the thermistor and other nearby components. If the issue is due to low refrigerant levels, recharge the system using manifold gauges to ensure proper pressure is maintained.

Important Notes:

• The P8 error code can also occur if the indoor unit fails to detect a temperature change within a set period after the compressor starts. Diagnosing this issue often involves checking the outdoor PC board for LED indications of the specific fault.
• Safety Warning: Working with electrical systems can be dangerous. Always consult a qualified technician or specialist to handle these repairs, especially if you are not experienced with HVAC systems​

Here is an article with a question-and-answer format about fixing the P8 error code on a Mitsubishi air conditioner:

How to Fix P8 Error Code on a Mitsubishi Air Conditioner

The P8 error code on a Mitsubishi air conditioner is typically related to an issue with the outdoor condenser unit. This error is quite generic and could indicate various problems ranging from wiring issues to component malfunctions.

Q1: What Does the P8 Error Code Mean on a Mitsubishi Air Conditioner?

A1: The P8 error code generally indicates that the indoor coil sensor did not detect a change in temperature within a set period (approximately 9 minutes) after the compressor was (or should be) switched on. Essentially, if the indoor unit does not get hot or cold within that time frame, it assumes the compressor is not running properly, triggering the P8 fault code​.

Q2: What are the Common Causes of the P8 Error Code?

A2: The P8 error can be caused by several issues, such as:

• Incorrect wiring or phase detection problems in three-phase systems.
• Sensor faults, where a sensor registers as open or short.
• High-pressure switch faults or refrigerant-related issues.
• Malfunctioning components, such as a faulty compressor or fan motor.

These issues are usually indicated by flashing LED lights on the outdoor unit’s PC board​(.

Q3: How Can I Troubleshoot the P8 Error Code?

A3: To troubleshoot the P8 error code, follow these steps:

1. Check the Outdoor Unit’s PC Board: Look for flashing LED lights to identify the specific issue.
   • LED 1 Flashing: Indicates a compressor command phase error. Check the wiring and ensure all phases are properly connected.
   • LED 3 Flashing: Indicates a pipe sensor short or open. Inspect and replace the faulty sensor if needed.
   • LED 6 Flashing: Suggests a 4-way valve issue or a faulty discharge thermistor. Test the thermistor and recharge the refrigerant if needed.
2. Inspect the Refrigerant Levels: Low refrigerant can cause high-pressure issues. Check for leaks and refill refrigerant using manifold gauges.
3. Test for Faulty Components: Components like fan motors, compressors, and sensors may need to be replaced if found faulty​.

Q4: Can I Fix the P8 Error Code Myself?

A4: It is generally not recommended to attempt DIY repairs on HVAC systems due to the complexity and risk involved. Electrical issues, in particular, should only be handled by a licensed technician. If you’re not experienced with HVAC systems, it’s best to consult a professional to avoid further damage or safety hazards​.

Q5: When Should I Call a Professional?

A5: If you have checked the basic issues like wiring and refrigerant levels and still see the P8 error code, it’s time to call a professional HVAC technician. They will have the tools and expertise to diagnose the issue correctly and ensure the problem is resolved without risking safety or causing further damage to the unit​.