Reefer trucking-thermo king unit. it cools normally when it is turned on to heat. suction pipe and port start freezing

It sounds like you're experiencing issues with your Thermo King cooling unit when it's set to heat mode. If the suction pipe and port are freezing, it could indicate a few potential problems. Here are some steps you can take to troubleshoot the issue: 1. **Check the Set Temperature:** Ensure that you have set the desired temperature correctly for heating. If it's set too low, the unit may try to cool instead of heat. 2. **Inspect the Thermostat:** The thermostat might be malfunctioning, causing the unit to cool instead of heat. Check if the thermostat is working as expected. 3. **Refrigerant Levels:** Incorrect refrigerant levels can lead to cooling when the unit is supposed to heat. Low refrigerant levels can cause the system to freeze up. You may need to have a technician check and adjust the refrigerant levels. 4. **Valve Issues:** There might be a problem with the reversing valve, which switches the unit between heating and cooling modes. If it's stuck or faulty, it can cause issues. A technician can inspect and repair this. 5. **Defrost Cycle:** If the unit has a defrost cycle, make sure it's working correctly. If it's not functioning, ice buildup can occur. 6. **Airflow and Filters:** Check for any obstructions in the airflow or clogged filters. Poor airflow can lead to freezing. 7. **Temperature Sensor:** The unit may have a temperature sensor issue. Ensure that the sensor is correctly placed and functioning. 8. **Maintenance:** Regular maintenance is crucial for the proper functioning of refrigeration units. Ensure that the unit is clean and well-maintained. 9. **Consult a Technician:** If you've checked these common issues and the problem persists, it's best to consult a professional technician or service provider who specializes in Thermo King units. They can diagnose the specific issue and perform any necessary repairs or adjustments. Remember that working with refrigeration systems can be complex and potentially hazardous. It's often best to have a qualified technician handle any repairs or adjustments to ensure the safety and effectiveness of your Thermo King unit.