Trane HVAC Error Code 4: How to Fix It

Q: What does Error Code 4 mean on a Trane HVAC system?

Trane Error Code 4 indicates a compressor under-current fault. This means the system's control board detected that the compressor is drawing less electrical current than the normal operating range. It typically points to a failed run capacitor, low refrigerant charge, an open compressor winding, or a loose electrical connection.

Q: Can I reset Trane Error Code 4 myself?

You can attempt a reset by turning the thermostat off, shutting off the breaker for 5 minutes, and then restoring power. However, a simple reset will not fix the underlying cause. If the root problem — such as a bad capacitor or low refrigerant — is not addressed, the error code will return. Always diagnose and resolve the cause before relying on a reset.

Q: How much does it cost to fix Trane Error Code 4?

Repair costs vary widely depending on the cause. Replacing a run capacitor typically costs $150–$400 including labor. Refrigerant recharge can range from $200–$600 depending on refrigerant type and the amount needed. If the compressor itself has failed, replacement costs can range from $1,200–$2,800 or more, and at that price point, replacing the entire outdoor unit is often worth considering.

Q: Is a compressor under-current fault dangerous?

Error Code 4 itself is a medium-severity fault and is not immediately dangerous in the way that a gas leak or fire hazard would be. However, operating the system repeatedly while this fault is active can stress the compressor further and lead to complete compressor failure, which is a much more expensive repair. Address this error promptly to avoid escalating the problem.

Q: How do I know if my Trane compressor is bad?

Signs of a failed Trane compressor include: the system runs but produces no cooling or heating, the compressor makes grinding, rattling, or clicking noises, the compressor does not start at all while the fan runs, and resistance testing of compressor windings shows an open or shorted circuit. A licensed HVAC technician can perform a definitive compressor diagnosis using professional gauges and test equipment.

Abstract

Trane HVAC Error Code 4 indicates a compressor under-current fault, meaning the compressor is drawing less electrical current than expected during operation. This can signal that the compressor is not starting properly, has an open winding, or is experiencing a loss of refrigerant that reduces its load. Left unaddressed, this error can lead to inadequate cooling or heating and potential long-term damage to the compressor.