What happens
The detection system reports refrigerant at its sensing location and activates its designed mitigation.
Typical symptoms
Refrigerant alarm with inhibited equipment or prescribed dissipation airflow.
Checks that distinguish this cause
Follow the unit's A2L response instructions, including area assessment and permitted test equipment. A qualified technician evaluates possible leakage; do not defeat mitigation to resume cooling.
What can look similar
A sensor fault has its own diagnostic definition, which must be confirmed rather than assumed.
Repair direction
Repair a confirmed leak and restore the detector and mitigation system using the approved process.
Verify the repair
Verify leak integrity and the OEM detector/mitigation checkout before return to service.
Equipment-specific limits
Treat a detection alarm as actionable until evaluated. Harness faults and actual refrigerant detection are different causes; neither is resolved by bypassing the sensor. Sensor faults can also initiate mitigation, depending on the equipment.
Practice this diagnosis
This cause is a reference topic; it does not yet have a dedicated simulated call. Browse the practice board.
References and applicability
Original HVACSim explanations with manufacturer and instrument-maker references for further reading. These resources support the subject; their model-specific examples are not specifications for every system.
- Carrier: HVAC installation and commissioning overviewSizing, airflow, charge and A2L installation considerations; obtain the exact unit manual.
- Trane: Precedent Symbio R-454B refrigerant leak sensor informationA model-specific example in which sensor faults and disconnection also initiate mitigation. Responses vary by equipment.
Editorial review: 2026-09-29. Verify the current manual for the installed model.