mypros+
Error code reference

Samsung Air Conditioner Error Code 321

EVI IN temperature sensor error (Open/Short)

Samsung codesSamsung air conditioner codes

EVI IN temperature sensor error (Open/Short) - connector dislocation, wire breaking, or defective sensor.

First step from the service manual

Check if EVI sensor is broken; check EVI sensor connection circuit and sensor.

The complete diagnostic procedure includes additional test steps, resistance specifications, wiring diagram references, and component test points.

MyPros+ Max

Get the full diagnostic procedure for 321.

  • Step-by-step tests with expected resistance, voltage, and continuity values
  • Wiring diagram references and connector pinouts from the OEM service manual
  • Verified part numbers when replacement is required
Get the full procedure

$29/month · Cancel anytime · Or $9.95 3-day pass

What 321 means on a Samsung air conditioner

Samsung air conditioner error code 321 indicates a fault in the EVI (Enhanced Vapor Injection) inlet temperature sensor circuit. The EVI system is a refrigerant injection circuit used in heat pump systems to improve efficiency and heating capacity at low ambient temperatures. The control board monitors the thermistor connected to the EVI inlet line to track refrigerant temperature entering the injection port. When the measured signal falls outside the expected resistance range, the system logs error 321 and may disable operation to prevent component damage.

The fault is classified as an open or short circuit condition in the sensor circuit. An open circuit occurs when the thermistor resistance rises beyond its valid range, typically due to a broken wire, corroded terminal, or a failed sensor element. A short circuit occurs when resistance drops abnormally low, often from wire insulation damage causing conductors to contact each other or a grounded surface. Both conditions produce a signal the control board cannot interpret as a valid temperature reading.

Diagnosis begins with a physical inspection of the EVI sensor and its wiring harness. Technicians should check the connector at the sensor and at the control board for proper seating, corrosion, or bent pins. If the connector is secure, measure the sensor resistance with a multimeter and compare it against the temperature-resistance chart for the installed thermistor. A sensor reading open or shorted at ambient temperature confirms sensor replacement is needed. If resistance reads correctly, trace the wiring for breaks or chafed insulation.

Source: manufacturer service documentation.

Common causes of 321

  1. 01

    Loose or dislodged sensor connector

    Wiring / connection

    Vibration during operation can cause the EVI sensor connector to partially or fully pull free from its socket on the control board or at the sensor body. Inspect both ends of the connector and reseat firmly until it clicks into place.

  2. 02

    Defective EVI temperature sensor

    Part replacement

    The thermistor element inside the sensor can fail open or short due to age, moisture intrusion, or thermal stress. Measure the sensor resistance with a multimeter and compare to the rated temperature-resistance curve. A reading of infinite resistance or near zero ohms confirms sensor failure.

  3. 03

    Broken or damaged sensor wire

    Part replacement

    The wiring between the EVI sensor and the control board can fracture internally while the outer insulation appears intact, especially near bends or cable clamps. Flex the wire along its length while monitoring resistance to identify intermittent breaks.

  4. 04

    Corroded or damaged connector terminals

    Part replacement

    Moisture entering the connector housing can oxidize the terminal contacts, increasing resistance and causing the control board to read an invalid signal. Inspect terminals visually and clean or replace the connector if corrosion is present.

  5. 05

    Shorted wiring from insulation damage

    Part replacement

    Chafed insulation where the harness contacts a metal edge or other wiring can create a short circuit condition. Trace the full length of the sensor harness and look for worn insulation or pinch points.

See the test procedure for each cause

Frequently asked questions about 321

What does 321 mean on a Samsung air conditioner?
Error code 321 on a Samsung air conditioner indicates a fault in the EVI inlet temperature sensor circuit. The control board has detected either an open or short circuit in the sensor, which can be caused by a disconnected connector, a broken wire, or a failed thermistor. The EVI system is used in heat pump models to enhance heating performance at low outdoor temperatures, so this fault can significantly impact heating capacity.
Can I fix error code 321 myself?
Some causes of error 321 can be addressed without specialized tools, such as reseating a loose sensor connector or inspecting visible wiring for obvious damage. However, confirming a sensor failure requires measuring thermistor resistance with a multimeter and comparing it to a temperature-resistance specification. Replacing the sensor or tracing internal wire breaks involves working inside the unit and is best handled by a qualified technician.
Is error code 321 on a Samsung air conditioner a safety issue?
Error 321 is a sensor circuit fault rather than a direct safety hazard to the home. However, operating the unit without a functioning EVI temperature sensor can prevent proper system control and may lead to refrigerant circuit issues over time. It is advisable to have the fault diagnosed and repaired promptly rather than continuing to run the system with the error active.
How much does it cost to repair error code 321 on a Samsung air conditioner?
Repair costs depend on the root cause. If the fix is simply reseating a connector, there may be little to no parts cost and only a service call fee, typically in the range of $75 to $150. If the EVI temperature sensor itself needs replacement, parts and labor combined can range from $150 to $350 or more depending on the model and local labor rates.
Will resetting the unit clear error code 321?
A power reset may temporarily clear the error code from the display, but if the underlying sensor fault is still present, the code will return once the control board re-evaluates the circuit. Resetting is useful for confirming whether a fault was intermittent, such as a connector that reseated on its own, but it does not repair a broken wire or failed sensor. A proper diagnostic check of the sensor and wiring is necessary to resolve the fault permanently.

Related Samsung air conditioner codes

All Samsung air conditioner codes
View all 572 Samsung air conditioner codes

78,000+ service manuals · 160,000+ error codes · 55+ brands

Get Started

$29/month · Cancel anytime · Or $9.95 3-day pass