Samsung Heat Pump Error Code E503

E503 indicates an open or short circuit fault on the indoor unit EVAP OUT sensor, which measures refrigerant temperature at the evaporator coil outlet. The PCB has detected a resistance signal outside the valid range for this sensor, so the system has shut down. The issue can be caused by a loose connector, a failed sensor, damaged wiring, or in some cases a faulty PCB.

No, the system will typically lock out and stop operating when E503 is active, and you should not attempt to bypass this lockout. The EVAP OUT sensor data is used to protect the refrigerant circuit and prevent conditions like coil icing or compressor damage. Continuing to run the unit without a functioning sensor could cause further component damage.

A power reset may temporarily clear the error code, but if the underlying sensor fault still exists the code will return as soon as the system attempts to read the sensor again. Resetting without repairing the sensor does not fix the problem and delays proper diagnosis. The error should be addressed by inspecting and testing the EVAP OUT sensor and its wiring before returning the unit to service.

A knowledgeable DIYer can check whether the sensor connector at the PCB has simply come loose and reseat it, which costs nothing and resolves some cases. If the connector is secure, diagnosing the sensor requires a multimeter to measure resistance across the terminals and interpret the reading. Replacing the sensor or PCB involves working inside the indoor unit and handling electrical components, so a qualified technician is recommended for those steps.

Costs vary depending on the root cause. If the fix is simply reseating a loose connector, there may be no parts cost and only a service call fee, typically in the range of $75 to $150. A replacement EVAP OUT sensor generally costs $20 to $60 for parts, with labor added on top. If the indoor PCB requires replacement, total repair costs can range from $250 to $600 or more depending on the unit model and labor rates in your area.