Fujitsu · Air Conditioner error code

42Indoor coil thermistor error

Cross-checked Power off, standard tools

Unlock what this code means, its causes, tests and parts

Full library + AI assistant for $34.90, one time.

OnCall Tech is a reference tool for trained technicians and can make mistakes. Always disconnect power and confirm with the manufacturer's documentation before you work.

Related diagnostic guides

Guide · Air Conditioner

Air conditioner freezing up (ice on the coil)

Ice forms when the coil gets too cold, nearly always from low airflow or running in cool weather. Thaw first, then fix airflow. Repeated icing with good airflow suggests low charge, which is sealed-system work.

5 steps ~60 mineasy

Guide · Air Conditioner

Mini-split indoor unit dripping water

Indoor head leaks are almost always drain related: clogged pan or line, poor line slope, a failed condensate pump, or the head not level. Ice on the coil from low airflow or low charge is the next suspect.

6 steps ~45 mineasy

Guide · Air Conditioner

Air conditioner dripping or leaking water indoors

Condensate is supposed to drain outdoors. Indoor leaks come from wrong tilt, blocked drain openings or lines, a frozen coil melting off, or a cracked pan / failed pump.

5 steps ~30 mineasy