System Diagnosis
24V sensing error (missing Y1 signal).
Trane | AC and Heat Pump
Error Code Red 18 Flashes
Troubleshooting guide for the Trane AC and Heat Pump system fault Red 18 Flashes.
Disclaimer: This information is for general reference. Error codes can vary by model and production year. Always refer to your machine's specific manual and the information printed on the unit itself.
Potential Causes & Solutions
- Verify the Y1 wire is firmly connected at the outdoor unit and thermostat.
- Ensure the thermostat is configured for two-stage cooling if applicable.
- Reset power after correcting wiring.
Diagnose with Confidence
Use the ACLogics AI assistant to walk through this error code step-by-step.
Included in Diagnosis Workflow
Ask
Upload nameplate & symptoms
Diagnose
AI identifies error Red 18 Flashes
Report
Generate professional PDF