Samsung Air Conditioner Error Code E477

Error code E477 on a Samsung air conditioner indicates a liquid compressor protection control event, specifically triggered when liquid refrigerant is detected flowing back into the digital compressor. Under normal operation, refrigerant should enter the compressor only in its vapor state. When liquid refrigerant migrates into the compressor suction port, it cannot be compressed and instead causes mechanical stress, oil dilution, and potential valve or piston damage. The control board activates this protective routine to halt or limit compressor operation before internal damage occurs.

The system uses the sump sensor and discharge sensor to monitor compressor conditions. The sump sensor tracks temperature at the base of the compressor where oil collects, while the discharge sensor monitors the high-side refrigerant temperature leaving the compressor. If these sensors report abnormal readings consistent with liquid refrigerant inflow, such as unusually low discharge temperatures or erratic sump readings, the E477 protection routine engages. Because faulty sensor connections can produce misleading data, the first diagnostic step is always to verify that both sensors are properly seated and making solid electrical contact.

Liquid refrigerant inflow, also called liquid slugging or flood-back, is commonly caused by refrigerant overcharge, low system load conditions, improper expansion valve operation, or prolonged off-cycle refrigerant migration into the compressor. In digital compressor systems, variable-speed operation at low capacity increases the risk of flood-back if refrigerant charge and expansion components are not correctly calibrated. Addressing E477 requires confirming sensor integrity first, then evaluating refrigerant charge level, expansion valve function, and operating conditions that may contribute to liquid carry-over into the suction line.