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Fujitsu · Heat pump

42 Indoor coil (heat exchanger middle) sensor error

Medium severity Fujitsu ductless split/multi/VRF (general code list)Fujitsu wall-mounted 7-15 (NA ASU/AOU type)Fujitsu slim duct ARU 7-18 (LL type)

What the control is telling you

The indoor coil thermistor reads open or shorted. Indoor lamps: OPERATION (green) flashes 4x, TIMER (orange) flashes 2x, ECONOMY (green) flashes fast nonstop; wired remote shows 42.

Applies to: Fujitsu ductless heat pumps: Fujitsu ductless split/multi/VRF (general code list), Fujitsu wall-mounted 7-15 (NA ASU/AOU type), Fujitsu slim duct ARU 7-18 (LL type)

Likely causes

  • Plug loose or wrong
  • Thermistor failure
  • Main PCB failure

Test and repair steps

  1. Check the sensor plug on the board is seated and on the right connector, and the lead is not cut or pinched.
  2. Unplug the thermistor and measure its resistance; compare with the resistance/temperature chart in the service manual. Open or shorted = replace.
  3. With the plug connected, check for about DC 5.0 V across the thermistor terminals on the board; no voltage = board fault.
  4. Cycle power after any repair and confirm the code does not return.

Settings for these units

Other codes on the same units

  • 33 Indoor fan motor power consumption error
  • 35 MANUAL AUTO button error
  • 39 Indoor fan motor power supply error
  • 41 Room (intake air) temperature sensor error
  • 44 Human (occupancy) sensor error
  • 51 Indoor fan motor error
  • 52 Indoor electronic expansion valve error
  • 53 Drain pump error

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Source: Fujitsu All Fujitsu split - multi - VRF (generic code list) codes.pdf - section error code table (indoor LED flashes); Fujitsu Wall-mounted 7-9-12-15 (North American trilingual, UTY-RNNUM remotes; e.g. ASU9-12-15 RLF1-RLS familie.pdf - section 14 Error codes; Fujitsu Wall-mounted KMCG (ASEH-AOEH 07-14) - Fujitsu UK; same error-code scheme as NA ASU-AOU units service S.pdf - section 3 Troubleshooting, 2 Troubleshooting with error code; Fujitsu Slim duct AR07-09-12-14-18 (ARU-ARYG LL-type equivalent) installation P-N 9381858064.pdf - section 14 Error codes. Summarized in our own words; check the original manual for your model.

Homeowner looking at this code? See what it means for you and when to call a technician.

For licensed technicians. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Shut off power and gas before servicing, never bypass a safety control, and follow the manufacturer’s manual for the exact model; it and local codes always take priority. HVACopedia is not affiliated with any manufacturer; brand and model names only identify the equipment.