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Air Conditioner Refrigerant charge and line set: What It Does and Signs It's Failing

The copper line set that links the indoor and outdoor units, the refrigerant inside it, and the service valves on the outdoor unit where the lines connect. Split systems are charged on site, so a poor install or a leaking flare joint shows up here.

How it works

Refrigerant flows through the lines in a closed loop, picking up heat indoors and releasing it outside (or the reverse in heat mode). Strainers in the line catch debris before it reaches the valves.

Signs it is failing

• Weak cooling or heating that gets worse over weeks
• Ice on the indoor coil or the smaller copper line
• Oily residue at a flare nut or on the copper lines
• Hissing near the line set
• Low refrigerant, low pressure or high discharge-temperature codes

Low refrigerant and low pressure codes, and some pipe-temperature codes, point here. If they show up right after installation or a move, LG says to call the installer back since piping or valves may be the cause.

Can you replace it yourself?

Check that the filters and both coils are clean, then shut the system off and call a pro if you see oil residue or ice. Never try a DIY recharge kit, loosen a flare nut or open a service valve. Leak hunting, brazing and recharging are refrigerant work, and in the US that legally needs an EPA Section 608-certified technician.

Buying the right part

No homeowner purchase here. Ask the tech to find and fix the leak rather than just topping it up, and to tell you what refrigerant the system uses.

Error codes linked to the refrigerant charge and line set

• U0Low refrigerant or restricted refrigerant flowDaikin
• A1Discharge temperature too highFujitsu
• A3Compressor temperature too highFujitsu
• A5Low pressure errorFujitsu
• E3Low pressure protectionGree
• E2Indoor coil freeze protectionGree
• CH38Low refrigerant protectionLG
• EL 0CPossible refrigerant leak detectedMidea
• P6Freeze or overheat protectionMitsubishi Electric
• P8Pipe temperature errorMitsubishi Electric
• U2Discharge temperature too high or low refrigerantMitsubishi Electric
• PLRefrigerant circuit abnormalMitsubishi Electric
• E554Refrigerant leak or low refrigerantSamsung
• E422Refrigerant flow blockedSamsung
• E416Compressor running too hotSamsung

Last reviewed 2026-10-19.