LG Heat Pump Error Code P784

P784 indicates an instant power off condition that occurs during the compressor startup sequence. The control system detects a loss or disruption of power at the moment the compressor attempts to start and initiates a protective shutdown. The code is self-clearing once the compressor successfully starts and runs, which helps narrow the fault to the startup phase specifically.

Because P784 disappears on its own once the compressor successfully runs, a power reset may temporarily clear the displayed code. However, if the underlying cause such as a weak capacitor or voltage supply problem is not corrected, the fault will return on the next startup attempt. A reset alone does not resolve the root cause.

Repair costs depend entirely on the root cause. A run capacitor replacement typically ranges from $75 to $200 including labor, while breaker replacement runs roughly $100 to $300 depending on amperage and panel access. If the compressor itself is drawing excessive startup current and needs replacement, costs can range from $800 to $2,500 or more. A diagnostic service call to identify the specific cause usually runs $75 to $150.

Some causes, such as a tripped breaker, loose disconnect connection, or low voltage from the utility, can be identified by a knowledgeable homeowner. However, diagnosing and replacing components like the run capacitor, contactor, or compressor involves working with high-voltage circuits and stored electrical charge, which carries serious safety risks. A qualified technician should handle any hands-on electrical testing or component replacement inside the unit.

The fault itself represents the control system doing its job by shutting down when it detects an abnormal power condition, which protects the compressor from damage. That said, repeated occurrences can indicate worsening electrical problems such as a deteriorating breaker or failing compressor that should be addressed promptly to avoid more costly damage or a potential electrical hazard.