Replacing Lost Matched (End-of-Line) Resistors 120 Ohms (0.5W) for Braemar VRF Outdoor Units


What is a Matched (End-of-Line) Resistor?

In a VRF (Variable Refrigerant Flow) air conditioning system, the indoor and outdoor units communicate through control wiring. To keep this communication clear and reliable, a matched resistor—also known as an end-of-line or terminating resistor—is installed at the end of the communication line.


Think of it like a walkie-talkie conversation: if the line isn’t properly closed off, the signal can bounce back like an echo, causing confusion in the system.


Why It’s Important

  • Prevents signal echo: Stops signals from bouncing back down the wire.
  • Ensures clear communication: Helps the system send and receive data without interference.
  • Avoids system errors: Missing or incorrectly placed resistors can cause communication faults or prevent the system from operating.


Issue (misplaced resistor supplied with outdoor unit pack-out kit)

Contractors may occasionally misplace the matched resistor included in the pack-out kit for VRF outdoor units. This component is essential for proper system communication.


Solution

If the resistor is lost, a replacement can be sourced from most electronics or electrical component suppliers.


Recommended Replacement Specifications:

Type: Resistor

Resistance: 120 Ohms

Power Rating: 1/2 Watt (0.5W)

Commonly sold in multi-packs

Refer to the example image below for visual reference. The coin is shown for size comparison only.


Installation Tip

Install the resistor at the end of the communication line, as shown in the VRF system’s wiring diagram. Incorrect placement or omission can lead to communication errors or system faults.


Example below


Important Reminder

Always refer to the specific installation manual for the product being installed.

Carefully check the schematic wiring diagrams for both Mains Power and Indoor-to-Outdoor communication connections to ensure correct and safe installation.


Troubleshooting Tips

If you're experiencing communication issues after replacing or reinstalling the resistor, try the following:

  • Check Resistor Value:

Use a multimeter to confirm it’s 120 Ohms.

  • Inspect Wiring:

Ensure all communication wiring is secure and undamaged.

  • Verify Resistor Placement:

It must be at the end of the communication line—not in the middle or at the controller.

  • Look for Shorts or Open Circuits:

Use a continuity tester to check for wiring faults.

  • Check for Duplicate Resistors:

Only one resistor should be installed at each end of the line. Multiple resistors can cause signal issues.

  • Power Cycle the System:

Restart the system after making changes to reset communication.

  • Consult the Wiring Diagram:

Always follow the manufacturer’s diagram for correct placement.



Additional Notes:

Always confirm the resistor value before installation.

Keeping a few spare resistors on hand is recommended to avoid delays during installation or servicing.