Troubleshooting E5/EH61 Error Code for MRCOOL Mini Split Air Handler Evaporator Coil Temperature Sensor

The E5/EH61 error code on a MRCOOL mini split system indicates a problem with the evaporator coil temperature sensor in the air handler. This sensor monitors the temperature of the evaporator coil to ensure proper cooling and heating operation. If this sensor malfunctions, it can disrupt the system’s ability to regulate temperature efficiently, triggering the error code. Below are the steps to troubleshoot this issue.

Step 1: Power Cycle the Unit

Start by performing a simple reset to see if the error code clears.

1. Turn off the power to the mini split system at the breaker.
2. Wait for at least 15 minutes to allow the system to reset.
3. Turn the power back on and monitor the system for any signs of the error code reappearing.

If the error clears, the issue may have been a temporary fault. If the code persists, proceed with further troubleshooting.

Step 2: Inspect the Evaporator Coil Temperature Sensor

If the error code persists, the issue likely lies with the evaporator coil temperature sensor itself.

1. Turn off the power to the mini split at the breaker to avoid electrical hazards.
2. Remove the air handler’s plastic cover to access the sensor, which is typically located near the evaporator coil inside the air handler.
3. Check for any visible signs of damage to the sensor or its wiring, such as fraying, corrosion, or loose connections.
4. Make sure the sensor is securely connected to the control board. A loose or poorly connected sensor can trigger the error code.

Step 3: Test the Sensor Using a Multimeter

You can test the evaporator coil temperature sensor with a multimeter to determine if it is functioning correctly.

1. Turn off the power to the mini split system.
2. Disconnect the sensor wiring from the control board.
3. Set the multimeter to measure resistance (Ohms) and connect the leads to the sensor wires. Make sure when taking the reading it does not show open leads. 
4. If the resistance is showing open leads, the sensor is likely faulty and should be replaced.

Step 4: Check the Evaporator Coil for Blockage

A blockage around the evaporator coil could also cause the sensor to malfunction or provide inaccurate readings, leading to an error code.

1. Inspect the evaporator coil for any signs of dirt, dust, or debris buildup.
2. Clean the coil if necessary to ensure proper airflow and sensor function.

A clean coil allows the sensor to more accurately monitor temperature changes, which helps prevent system malfunctions.

Step 5: Inspect the Air Handler Control Board

If the sensor appears to be in good condition and the wiring is secure, the issue could be related to the air handler's control board.

1. Turn off power to the system and inspect the control board for any visible signs of damage, such as burn marks, corrosion, or loose wiring.
2. If the control board appears damaged, it may need to be replaced.

Step 6: Verify Proper Refrigerant Levels

A refrigerant issue can also cause the evaporator coil to malfunction, which may trigger the E5/EH61 error code.

1. Contact a licensed HVAC technician to check the refrigerant levels.
2. If the system is low on refrigerant, it could affect the cooling process and lead to incorrect readings from the evaporator coil temperature sensor.

Step 7: Contact MRCOOL Support

If none of the troubleshooting steps resolve the issue, it’s advisable to contact MRCOOL customer support or a professional HVAC technician. They can provide more advanced diagnostics and repair options.

Conclusion

An E5/EH61 error code in MRCOOL mini split systems usually points to a problem with the evaporator coil temperature sensor, which plays a key role in regulating the temperature inside the system. By following these troubleshooting steps—ranging from checking connections and cleaning the coil to testing the sensor with a multimeter—you can often identify and resolve the issue. If the error persists, professional assistance may be needed to ensure your system is running smoothly.