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Error Code
E5 points at the compressor. The system has decided it is not running as it should, which covers a failed winding, a mechanical seizure and an electrical fault in the circuit feeding it. This is the code that leads to the biggest quote in the Fujitsu range, and it is also the one where a rushed diagnosis costs the most, so the tests get done in order.
Current rises when the compressor is working harder than it should, whether from a refrigerant circuit that is not flowing, a condenser that cannot reject heat, or a bearing that is tightening inside the shell. The protection sees the current and cuts the supply. Where the reading sits at start and during steady running tells a technician which of those it is.
Windings fail from heat and age, and the failure is often progressive rather than instant. A compressor drawing slightly more current each season is on its way out long before it stops. Resistance measured across the windings and insulation resistance measured to earth are what confirm it, and both are done before a replacement is quoted.
A pitted contactor, a terminal that has been running hot or insulation breaking down will produce E5 on a compressor that is mechanically perfect. These faults are cheap to fix and are routinely mistaken for a failed compressor, which is why the electrical checks come before the expensive conclusion.
Winding resistance is measured across each phase and compared with the manufacturer figures and with the other phases. Insulation resistance to earth is measured next. A winding that is open, shorted or leaking to earth confirms the compressor. Anything else means the fault is in the circuit around it, not in the compressor.
Contactor points, terminal blocks and the cable run are inspected for pitting, heat discolouration and looseness. A contactor with burnt points introduces resistance and heat, and the compressor sees a supply that sags exactly when it needs current most. Replacing it costs a fraction of the compressor it is protecting.
With the power off the compressor is checked mechanically as well as electrically: whether the terminal block is intact, whether there is any sign of a refrigerant leak at the seals, and whether the windings behave as they should when measured. Testing rather than assuming is what stops a serviceable compressor being condemned.
