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Error code reference

Samsung Air Conditioner Error Code P404

Low pressure switch detection

Samsung codesSamsung air conditioner codes

Low pressure switch detection – operation stop when low pressure is lower than 1.2 kg/cm²G (sensor open); system down on 2nd detection.

First step from the service manual

Check if both service valves are open.

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

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What P404 means on a Samsung air conditioner

The P404 error code on a Samsung air conditioner indicates that the low pressure switch has detected a suction pressure drop below the critical threshold of 1.2 kg/cm²G. This threshold represents the minimum acceptable refrigerant pressure on the low-pressure side of the refrigeration circuit. When pressure falls below this level, the low pressure switch opens its contacts, signaling the control board to halt compressor operation to prevent damage. The system is designed to stop immediately upon detection to protect the compressor from running in a starved or low-refrigerant condition.

The system applies a two-detection logic before executing a full system shutdown. On the first detection, operation stops temporarily. If the condition is detected a second time, the unit enters a locked-down fault state, which requires manual intervention to clear. This escalating response is designed to distinguish between brief transient pressure drops and persistent system faults that could indicate serious refrigerant circuit problems.

The most common root causes include closed or partially closed service valves, refrigerant leaks causing low charge, a faulty low pressure switch that has failed in the open position, or a blocked metering device such as a clogged expansion valve or filter drier restricting refrigerant flow. A dirty or iced evaporator coil can also reduce system pressure by limiting heat absorption. Because the low pressure switch is an open-circuit signal, the control board interprets either a genuine pressure drop or a failed open switch as the same fault condition, so component testing is necessary to isolate the root cause.

Source: manufacturer service documentation.

Common causes of P404

  1. 01

    Service valve closed or partially closed

    Wiring / connection

    If either the liquid or suction service valve is not fully open, refrigerant flow is restricted and low-side pressure drops rapidly. This is the first thing to check and requires no parts, only valve adjustment.

  2. 02

    Low refrigerant charge due to a leak

    Part replacement

    A refrigerant leak reduces system charge over time, causing suction pressure to fall below the 1.2 kg/cm²G threshold. A manifold gauge set will confirm low suction pressure, and leak detection is required to find the source before recharging.

  3. 03

    Faulty low pressure switch

    Part replacement

    The low pressure switch may have failed in the open position, causing the control board to read a fault even when system pressure is normal. Continuity testing across the switch terminals while the system is running can confirm whether the switch itself is defective.

  4. 04

    Blocked expansion valve or filter drier

    Part replacement

    A clogged expansion valve or saturated filter drier restricts refrigerant flow into the evaporator, causing suction pressure to drop below the fault threshold. Ice formation at the restriction point or abnormal temperature differentials across the component can help identify this cause.

  5. 05

    Iced or heavily fouled evaporator coil

    Wiring / connection

    Restricted airflow across the evaporator due to ice buildup or heavy dirt accumulation reduces heat absorption, causing refrigerant to remain mostly liquid and suction pressure to fall. Inspecting the evaporator coil for frost or blockage is a straightforward visual check.

See the test procedure for each cause

Frequently asked questions about P404

What does P404 mean on a Samsung air conditioner?
P404 indicates that the low pressure switch has detected refrigerant suction pressure below 1.2 kg/cm²G, which is the minimum safe operating pressure for the compressor. When this threshold is crossed, the unit shuts down to prevent compressor damage. If the condition is detected a second time, the system enters a full lockout state and will not restart without manual intervention.
Can I fix a P404 error myself?
Some steps can be checked without special tools, including confirming that both service valves are fully open and inspecting the evaporator coil for ice or heavy fouling. However, diagnosing a refrigerant leak, testing the low pressure switch, or recharging the system requires EPA certification and professional equipment. Most P404 repairs beyond valve checks should be handled by a licensed HVAC technician.
Is it safe to keep running my air conditioner with a P404 error?
No. The P404 error means the system has already shut itself off to protect the compressor. Attempting to bypass or ignore this fault and force operation with low refrigerant pressure can cause the compressor to run unlubricated, leading to permanent compressor failure. Leave the unit off until the underlying cause is diagnosed and corrected.
Will resetting the air conditioner clear the P404 error?
A reset may temporarily clear the fault display, but the error will return if the underlying pressure problem has not been resolved. After two detections of the low pressure condition, the system enters a locked shutdown state that will not clear until the root cause is addressed. Repeated resets without fixing the problem risk compressor damage.
How much does it cost to repair a P404 error on a Samsung air conditioner?
Repair costs vary widely depending on the cause. Confirming open service valves costs nothing, while replacing a faulty low pressure switch typically runs in the range of $100 to $250 including labor. A refrigerant leak repair combined with recharging the system can range from $200 to $600 or more depending on leak location and refrigerant type. Compressor replacement, if damage has already occurred, can cost $800 to $2,000 or higher.

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