Cause : Motor overheat (PTC/NTC thermistor) comes when the temperature of the motor has risen abnormally. The connected motor has exceeded its safe operating temperature. This fault is essential to protect both the motor and the drive from damage.

"Oh4" fault in Fuji FRENIC-VG drive indicate "Motor overheat". This means the motor temperature has exceeded safe operating limits. This fault is triggered by a motor temperature sensor (often a thermistor or RTD) or by the drive's estimation of motor temperature based on current, load, and operating conditions.

Troubleshooting Steps:

1. Check the Motor Load:

   • Verify that the motor is not overloaded. Reduce the load if it exceeds the motor's rated capacity.
   • Inspect the connected load for any mechanical issues, such as binding or excessive friction, that could be causing the motor to work harder and generate more heat.

2. Inspect Cooling Systems:

   • Ensure that the motor's cooling fans are functioning properly. Replace any faulty fans.
   • Check for any obstructions in the motor’s ventilation paths. Clean out any dust, dirt, or debris that may be blocking airflow.
   • If the motor has a separate cooling system (e.g., an external fan or heat exchanger), ensure it is working correctly.

3. Verify Ambient Conditions:

   • Measure the ambient temperature around the motor and ensure it is within the specified operating range.
   • If the environment is too hot, consider improving ventilation, adding air conditioning, or relocating the motor to a cooler area.

4. Review Drive Settings:

   • Check the drive’s motor protection settings, such as thermal overload protection, current limits, and acceleration/deceleration times. Ensure they are configured correctly for the motor being used.
   • Adjust the settings if necessary to prevent the motor from overheating under normal operating conditions.

5. Inspect the Motor’s Temperature Sensor:

   • If the motor has an internal temperature sensor, check its connection and ensure it is functioning correctly.
   • Test the sensor for accuracy using a multimeter or other diagnostic tools. If the sensor is faulty, it may need to be replaced.