Johnson Controls MR4PMUHV-12C Defrost Control User Manual

1. Introduction

The Johnson Controls MR4PMUHV-12C Defrost Control is engineered for use in refrigeration and freezer units, supporting both hot gas and electric heat defrost methods. This control unit offers flexible defrost termination options, allowing selection between time-based or temperature-based methods. It integrates essential control functions including compressor management, defrost cycle management, fan operation control, and alarm management, providing a comprehensive solution for HVAC systems.

Figure 1: Johnson Controls MR4PMUHV-12C Defrost Control unit and included temperature sensors. The central gray unit features a digital display and control buttons, while two coiled gray cables with metallic tips represent the temperature sensors.

2. What's in the Box

• Johnson Controls MR4PMUHV-12C Defrost Control Unit
• Temperature Sensors (2 units)

3. Key Features

• Integrated Functionality: Combines multiple control functions into a single unit, offering a cost-effective solution.
• Flexible Mounting: The control unit and relay pack can be mounted together or separately to suit various installation requirements.
• Accurate Temperature Sensing: Utilizes interchangeable temperature sensors for reliable performance, supporting wiring up to 300 ft. with offset compensation for longer runs.
• Clear Temperature Display: An easily readable display shows either evaporator or process temperature at the press of a button.
• Heavy-Duty Relays: Equipped with robust relays for direct control of compressors, fans, defrost heaters, and alarm systems.

4. Setup and Installation

Proper installation is crucial for the safe and efficient operation of the defrost control. Always ensure power is disconnected before beginning any installation or wiring procedures.

1. Safety First: Disconnect all power to the refrigeration or freezer unit before proceeding. Follow all local electrical codes and safety guidelines.
2. Mounting: Select a suitable location for mounting the control unit and, if applicable, the separate relay pack. Ensure adequate ventilation and protection from moisture. The flexible design allows for combined or separate mounting.
3. Wiring Connections:
   • Connect the 24VAC power supply to the designated terminals on the control unit.
   • Wire the compressor, fans, and defrost heaters to the heavy-duty relay terminals as per the wiring diagram provided with the product.
   • Connect any external alarm systems to the dedicated alarm terminals.
4. Sensor Installation: Install the temperature sensors in the appropriate locations within the evaporator or process area as required for accurate temperature monitoring. Ensure sensor cables are routed safely and securely.
5. Initial Power-Up: Once all connections are secure and verified, restore power to the unit. The control unit display should illuminate.

5. Operation

After successful installation, the MR4PMUHV-12C is ready for configuration and operation.

1. Display Overview: Upon power-up, the digital display will show the current temperature. Pressing the designated button (refer to product-specific labeling) allows toggling between evaporator and process temperature readings.
2. Setting Defrost Parameters: Access the control unit's menu (typically via dedicated buttons) to configure defrost settings. This includes:
   • Defrost Interval: Set the frequency at which defrost cycles occur.
   • Defrost Duration: Specify the maximum time for a defrost cycle.
   • Defrost Termination Method: Choose between time-based termination (defrost ends after a set duration) or temperature-based termination (defrost ends when a specific temperature is reached).
   • Fan Delay: Configure any fan delay settings post-defrost.
3. Alarm Settings: Configure temperature thresholds for alarms to ensure optimal operating conditions and prompt notification of deviations.
4. Monitoring: Regularly check the display for current temperatures and system status.

6. Maintenance

Routine maintenance helps ensure the longevity and reliable performance of your defrost control unit.

• Cleaning: Periodically clean the exterior of the control unit with a soft, dry cloth. Avoid using abrasive cleaners or solvents.
• Wiring Inspection: Annually inspect all wiring connections for tightness and signs of wear or corrosion. Ensure all connections are secure.
• Sensor Check: Verify that temperature sensors are securely in place and free from damage. Ensure their placement continues to provide accurate readings.
• Functionality Test: Periodically observe the defrost cycles to confirm they are initiating and terminating correctly according to programmed settings.

7. Troubleshooting

This section provides guidance for common issues. For complex problems, contact qualified service personnel.

• Unit Not Powering On:
  • Check the 24VAC power supply connection.
  • Verify that the circuit breaker or fuse supplying power to the unit is not tripped or blown.
• Incorrect Temperature Readings:
  • Ensure temperature sensors are correctly installed and not damaged.
  • Check sensor wiring for loose connections or breaks.
  • Verify sensor calibration if possible (refer to advanced settings).
• Defrost Cycle Not Initiating/Terminating:
  • Review defrost interval and duration settings in the control unit's menu.
  • Confirm the selected defrost termination method (time or temperature) is appropriate for the application.
  • Check wiring to defrost heaters or hot gas valve.
• Alarms Activating Unexpectedly:
  • Verify alarm setpoints are correctly configured.
  • Check for actual temperature deviations that might be triggering the alarm.

8. Specifications

9. Warranty and Support

For information regarding product warranty, technical support, or service, please contact Johnson Controls directly or refer to the official documentation included with your purchase. Keep your proof of purchase for warranty claims.

Johnson Controls Contact Information: Please visit the official Johnson Controls website for the most current contact details and support resources.