System Diagnosis
Outside Air Temperature Failure. Outside-air temperature is outside the valid range; usually caused by faulty thermistor, wiring error, or loose connection.
Carrier | Outdoor Packaged Units
Error Code 73
Troubleshooting guide for the Carrier Outdoor Packaged Units system fault 73.
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
- Check OAT sensor wiring, connector, and routing.
- Measure sensor resistance and compare to chart.
- Inspect for wiring errors or open circuits.
- Replace OAT thermistor if resistance is outside specifications.
Verify Before Replacing Parts
- Confirm the exact Carrier model family and outdoor packaged units context before acting on a generic code description.
- Verify the sensor or thermistor reading against the expected range for the current operating condition.
- Check the sensor harness and board connection before condemning the sensor itself.
- After the correction, run the system long enough to confirm the code does not return under normal load.
Field Signals to Confirm
What usually confirms it
Sensor values that do not match the operating condition or drift when the harness is moved.
What can fool you
A control board issue can look like a failed sensor if the reference voltage or connector is unstable.
When to Escalate the Call
- Sensor values remain unstable after connector and board checks.
- The model uses a proprietary sensor curve you cannot verify confidently in the field.
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 isolates the likely outdoor packaged units branch behind code 73
Report
Document the verified result and next action