Samsung Heat Pump Error Code E604

E604 indicates an indoor unit EEV (Electronic Expansion Valve) open error on its first detection. The system has determined that the EEV is not moving correctly or is failing to close, which can allow refrigerant to flow into a stopped indoor unit. This fault involves the EEV itself, its wiring harness, or the indoor PCB that controls it.

Continuing to operate the system with an E604 error is not recommended. A stuck-open EEV allows refrigerant to migrate into a stopped indoor unit, which can cause liquid refrigerant flooding, compressor damage, and reduced system efficiency. Shutting the system down and scheduling a service call promptly will help prevent more extensive damage.

A power reset may temporarily clear the E604 error code, but if the underlying problem with the EEV or its wiring has not been resolved, the fault will return. The E604 is flagged as a first detection event, meaning continued operation without repair may lead to additional fault codes or escalating damage. A proper diagnosis and repair is needed for a lasting resolution.

The first step, checking whether the EEV wire harness is securely connected to the indoor PCB, is something a knowledgeable DIYer can inspect visually. However, further diagnosis involving refrigerant handling, coil resistance testing, or component replacement should be performed by a certified HVAC technician, as working with refrigerant requires proper licensing and equipment.

Repair costs depend on the root cause. A loose wire connection may only require a service call fee, typically in the range of $75 to $150. Replacing a faulty EEV or its coil can cost between $150 and $450 in parts and labor. If the indoor PCB needs replacement, costs can range from $300 to $600 or more depending on the unit model.