LG Heat Pump Error Code P509

P509 means the compressor has been shut down by the system's high pressure sensor protection control, specifically classified as protection event 3. The refrigerant pressure on the discharge side of the system exceeded a safe threshold, and the unit stopped the compressor to prevent damage. The underlying cause must be identified and corrected before the system will run reliably again.

No. The P509 fault causes the compressor to shut down specifically to prevent damage from excessive refrigerant pressure. Attempting to force the system to operate without resolving the root cause risks compressor failure, refrigerant line stress, and potential safety hazards. Leave the unit off until the cause is diagnosed and repaired.

Repair costs vary widely depending on the cause. A coil cleaning or filter replacement may cost between $75 and $200 for a service call. Fan motor replacement typically runs between $200 and $500 including parts and labor. If the compressor has sustained damage or refrigerant correction is needed, costs can range from $300 to over $1,000 depending on system size and refrigerant type.

Some contributing factors, like a dirty outdoor coil or a clogged air filter, can be addressed by a homeowner with basic maintenance skills. However, diagnosing refrigerant charge issues, testing pressure sensors, or replacing fan motors requires proper tools and in the case of refrigerant work, EPA certification. It is best to have a licensed HVAC technician perform a full system evaluation if the error returns after cleaning and airflow checks.

A power reset may temporarily clear the fault and allow the unit to restart, but if the underlying condition causing high pressure has not been resolved, the error will return quickly. Repeated cycling without a fix can accelerate compressor wear. A reset should only be performed after addressing the suspected cause, not as a standalone solution.