Carrier HVAC Error Code 46

Error code 46 on a Carrier HVAC system indicates a brownout condition on the control transformer secondary circuit. The secondary voltage dropped below 15Vac and stayed there for more than four seconds, triggering the fault. The system will clear this code automatically once secondary voltage rises above 17Vac for more than four seconds. No manual reset is required if the underlying voltage issue resolves on its own.

Start by measuring the secondary voltage at the control transformer output terminals with a multimeter set to AC voltage. If the reading is below 15Vac under load, check the low-voltage wiring for shorts, inspect all accessories connected to the secondary circuit, and test the transformer itself. A failed or undersized transformer will need to be replaced, while a wiring short will need to be located and repaired.

Repair costs depend heavily on the cause. If the issue is simply a loose connection or corroded terminal, the labor cost for a service call is typically the primary expense, often in the range of $75 to $200 depending on your area and technician rates. Replacing a control transformer generally adds $50 to $150 in parts. If the fault stems from a more complex wiring problem or damaged control board, total costs could range from $200 to $600 or more.

Yes, error code 46 is a self-clearing fault. Once the secondary transformer voltage rises above 17Vac and remains there for more than four seconds, the condition clears automatically and the system resumes normal operation. If the fault keeps returning, it means the underlying voltage problem has not been corrected and further diagnosis is needed.

The fault itself is a protective condition, not an emergency hazard. The system is designed to detect low secondary voltage and stop operating to prevent control board damage or erratic behavior. However, the root cause such as a shorted wire or failing transformer should be diagnosed and corrected promptly to avoid further damage to the control circuit components.