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Error Code
F5 points at the compressor motor. The system has decided the compressor is not running as it should, which can mean a failed winding, a mechanical seizure or an electrical fault in the circuit feeding it. This is the most expensive code in the Carrier range, which is exactly why the diagnosis must be finished before anyone quotes for a compressor.
Windings fail from heat, from age, or from years of running on a supply that sags under load. A compressor with a failing winding often draws higher current than it should before it stops altogether. Winding resistance and insulation resistance identify it, and both are measured before the compressor is condemned.
Current climbs when the compressor works harder than it should, whether from a mechanical bind, a restricted refrigerant circuit or a condenser that cannot reject heat. The protection sees the rise and cuts out. Measuring current at start and in steady running tells a technician which of those is happening on this unit.
Short circuits, a loose terminal or insulation breaking down produce F5 on a compressor that is mechanically sound. These are the faults worth finding first, because they cost a fraction of a compressor and they are routinely mistaken for one. Insulation resistance testing is what separates them cleanly.
Turn the unit off for five to ten minutes to reset the protection, then restart while watching and listening. A compressor that hums and trips within seconds behaves nothing like one that runs for twenty minutes and then stops. Note which it does before it trips, because that observation is worth more than any single meter reading.
Winding resistance is measured across each phase and insulation resistance to earth, then compared with the manufacturer’s figures. A winding that differs from its siblings, or one that leaks to earth, has failed. This is the test that decides whether the compressor is replaced or the fault sits somewhere else.
Contactor points, terminal blocks and the cable run are inspected for pitting, heat discolouration and looseness. A contactor with burnt points adds resistance and heat, and the compressor sees a supply that sags under load. Replacing it costs a fraction of the compressor it protects.
