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Troubleshooting code

Back to all 5TDM5B03AC21 error codes

Trane 5TDM5B03AC21 Running 3s 1 flash troubleshooting

Indoor/outdoor communication or jumper cap failure. Use this page to document the issue and prepare for service. GreenFlow should handle diagnosis for electrical, refrigerant, lockout, or recurring conditions.

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What the code means

Running 3s 1 flash: Indoor/outdoor communication or jumper cap failure

Trane AHR-SVX008A-EN LED indicator system-failure table for 5TDM5 air handlers identifies running indicator light out for 3 seconds then flashing once as indoor/outdoor communication error or indoor jumper cap failure.

System area
Indoor and outdoor communication
Service level
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Safe checks before calling

  • Confirm the thermostat is on, set correctly, and calling for heating or cooling.
  • Check the air filter and visible return-air path for obvious airflow restrictions.
  • Look around the outdoor unit for leaves, snow, ice, or other visible obstructions without opening the cabinet.
  • Take photos of the thermostat, outdoor unit, nameplate, and any visible flash pattern before scheduling service.

When to stop and call GreenFlow

Call GreenFlow if the code repeats, the system is locked out, heating or cooling is not restored, there is ice buildup, electrical odor, unusual noise, or any issue involving pressure switches, sensors, wiring, refrigerant, reversing-valve operation, or warranty coverage.

Share the visible code, model and serial number if available, photos, current symptoms, and whether the issue affects heating, cooling, or both.

Running 3s 1 flash questions

What does Running 3s 1 flash mean on a Trane 5TDM5B03AC21?

Trane AHR-SVX008A-EN LED indicator system-failure table for 5TDM5 air handlers identifies running indicator light out for 3 seconds then flashing once as indoor/outdoor communication error or indoor jumper cap failure.

What should I safely check before scheduling service?

Check thermostat status, filter condition, visible outdoor-unit obstructions, and take photos of the flash pattern and nameplate. Do not open electrical panels or refrigerant-side components.

When should GreenFlow handle this code?

Call GreenFlow if the code repeats, the system is locked out, heating or cooling is not restored, there is ice buildup, electrical odor, unusual noise, or any issue involving pressure switches, sensors, wiring, refrigerant, reversing-valve operation, or warranty coverage.

Need help with this code?

GreenFlow can review the code, photos, equipment access, and symptoms before scheduling the right next step.

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