How to Check MRCOOL Inverter Error Code: A Comprehensive DIY Guide

Troubleshooting MRCOOL inverter error codes can be a daunting task, but with the right knowledge and tools, you can diagnose and resolve the issue efficiently. This comprehensive guide will walk you through the step-by-step process of checking MRCOOL inverter error codes, providing you with the technical expertise and practical insights to tackle the problem head-on.

Identify the Error Code

The first step in resolving a MRCOOL inverter error is to accurately identify the error code displayed on the unit’s control panel. Common MRCOOL inverter error codes include:

  • P1: Compressor high pressure protection
  • P4: Compressor low pressure protection
  • E1: Indoor and outdoor unit communication error
  • EL 01: Compressor overload protection

Accurately identifying the error code is crucial, as it will determine the appropriate troubleshooting steps to follow.

Check the Voltage

how to check MRCOOL inverter error codeImage source: nan

If the error code is P1 or P4, you can proceed to check the voltage of the unit using a multimeter. For a unit running on 120 volts, touch the multimeter leads to L1 and ground. For a unit running on 240 volts, touch the leads to L1 and L2.

If the voltage is not within the recommended range, it may indicate a wiring issue or a problem with the unit’s power supply. Ensure that the voltage is stable and within the manufacturer’s specifications to rule out any power-related problems.

Inspect the Wiring

If the error code is related to communication between the indoor and outdoor units, such as E1, you should check the wiring on both units to ensure that the wire numbers match the connections. Use a voltmeter to measure the AC voltage between L1 and L2 on the condenser, as well as between wires 1 and 2 going to the air handler.

If the voltage is within the recommended range, it may indicate a problem with the control board. Proceed to the next step to further investigate the control board.

Analyze the Control Board

If the voltage is within the recommended range, but the error code persists, you can measure the DC voltage between the black leads on terminals 2 and 3, and the red lead on terminal 3. If the value is fixed and close to zero, it may indicate a problem with the wiring connection from the indoor terminal to the indoor primary control board. If the value is alternating between negative and positive, it may suggest an issue with the indoor primary control board.

To accurately diagnose the control board, it’s essential to have a thorough understanding of the unit’s electrical schematics and the specific voltage ranges for each component.

Contact Technical Support

If you have exhausted all the troubleshooting steps and are still unable to resolve the error code, it’s time to reach out to MRCOOL’s technical support team. They can provide expert guidance, help you diagnose the problem, and offer solutions on how to fix the issue.

Remember, working with electrical systems can be dangerous, so if you are not comfortable performing these steps on your own, it’s highly recommended to contact a professional HVAC technician for assistance.


By following this comprehensive guide, you’ll be equipped with the knowledge and tools necessary to effectively check and troubleshoot MRCOOL inverter error codes. Remember to always prioritize safety, and don’t hesitate to seek professional help if you’re unsure about any step in the process. With the right approach, you can quickly identify and resolve the issue, ensuring your MRCOOL unit operates at its optimal performance.


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