Daikin [E6] fault codewhat it means and how to fix it

E6 is published by Daikin under the OUTDOOR UNIT heading as faulty compressor start-up. The compressor is the part that actually does the work in an air conditioner — everything else moves air or moves refrigerant around it — so a compressor that will not start means a system that will not cool, however healthy the rest of it looks. The indoor unit will usually carry on blowing, which is what makes this present as poor performance rather than a breakdown. A compressor can fail to start for reasons that range from cheap to terminal, and the distinction is not something you can make from the garden.

Daikin’s service manual calls this code Compressor Lock, detects it from the current waveform when the inverter applies a high-frequency voltage to the motor, and gives three supposed causes: a closed stop valve, a locked compressor, and a disconnected compressor harness. Only the middle one is the compressor itself. A stop valve left closed or partly closed after installation or service work will produce it on a perfectly good machine, and a harness or the board driving it is an electrical repair rather than a compressor. These are inverter compressors driven directly by the outdoor board, so there is no start capacitor to fail — the electrical end of the list is the harness and the board. It may be mechanical, where the compressor is seized or the motor windings have failed, which is the expensive end. Or it may be a protective refusal, where the system has detected conditions under which starting would cause damage and has declined. That last case is why the codes around it matter.

Daikin publish a cluster of related outdoor unit faults, and they belong to the same conversation: E5 for an overload having started, F3 for high discharge pipe temperature, F6 for high pressure control in cooling, L5 for output overcurrent, and L4 for high temperature at the inverter heatsink. Several of those point at conditions rather than components — a system that is overheating, over-pressured or drawing too much current is often reacting to something else, such as restricted airflow at the outdoor unit or a refrigerant problem. What you can usefully do before calling anybody is limited but not worthless. Confirm the outdoor unit has clear space around it and is not smothered by planting, fencing or debris, because a unit that cannot reject heat will trip protections repeatedly. And note whether the fault is intermittent or permanent, because that genuinely helps. Beyond that, this is inside a sealed refrigerant circuit and a mains electrical enclosure.