The “Electrical Surge” Problem
The L5 Error is the safety mechanism that saves your house from a fire. The Outdoor PCB constantly monitors the current sent to the Compressor via the U, V, and W wires.
The Trigger: If the compressor tries to pull more current (Amps) than allowed—even for a millisecond—the PCB cuts power instantly and displays L5. This usually happens because the compressor is jammed (mechanical lock) or the electronics driving it have short-circuited.
1 Basic Checks (Before the Expensive Stuff)
Service Valves Closed?
Did you just install the AC? If the Allen key valves on the outdoor unit are closed, the compressor pumps against a wall, overloads, and trips L5 instantly.
Short Circuit in Wires
Inspect the U-V-W wires connecting the PCB to the compressor. If insulation has melted and wires are touching, L5 will occur.
Outdoor Fan Stuck?
If the outdoor fan isn’t spinning, the heat isn’t removed. High pressure builds up, the compressor works too hard, and trips L5.
Atlas Aircon Diagnostics
We find the culprit (PCB vs Compressor):
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01.
Compressor Megger Test We unplug the compressor and test the windings against the body ground. If resistance is zero (Grounded), the compressor is dead.
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02.
PCB “IPM” Output Check We run the AC without the compressor connected. If L5 still appears immediately, the Power Module on the PCB is blown.
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03.
Refrigerant Pressure If both parts are fine, we check for over-gas (too much pressure) or a blocked capillary tube causing the overload.
Estimated Repair Cost (Atlas Aircon)