LG Air Conditioner Error Code E451

E451 indicates a low pressure switch fault on the second detection circuit of the refrigerant system. The unit has detected that suction pressure has dropped below a safe operating threshold and has shut the compressor down to prevent damage. This fault most commonly points to a low refrigerant charge caused by a leak, though a faulty pressure switch or a refrigerant restriction can also trigger it.

No. The E451 fault causes the unit to shut down the compressor specifically to prevent mechanical damage from low-pressure operation. Repeatedly attempting to restart and run the system without addressing the root cause can lead to compressor failure, which is a significantly more expensive repair. Leave the unit off until the fault is diagnosed and corrected.

A power reset may temporarily clear the fault display, and the unit may attempt to restart. However, if the underlying cause such as low refrigerant charge or a faulty pressure switch has not been corrected, the E451 fault will return quickly once the system tries to operate. A reset is useful for confirming the fault is active and repeatable, but it is not a repair.

Some preliminary checks, such as verifying that service valves are open and that ambient temperatures are within the unit's operating range, can be done without special tools. However, diagnosing and repairing the most common cause, a refrigerant leak, requires EPA-certified technicians and specialized equipment in most regions. Replacing a low pressure switch also involves recovering refrigerant, so professional service is strongly recommended for this fault.

Repair costs vary widely depending on the cause. Refrigerant leak detection and recharge can range from around 200 to 600 dollars or more depending on leak location, system size, and refrigerant type. A low pressure switch replacement is generally less expensive, typically in the range of 100 to 300 dollars including labor. If a refrigerant restriction requires replacing the filter drier or expansion valve, costs can be higher.