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Carrier · Heat pump

56 OAT / coil thermistor out of range

Medium severity Carrier Infinity 18VS 25VNA8Carrier 2-stage 24ANB/25HNBCarrier single-stage communicating HP

What the control is telling you

Amber STATUS light flashes 56. Outdoor air and outdoor coil temperatures do not make sense together, e.g. the coil shows heating while cooling is called. Type: Event; reset: None.

Applies to: Carrier Infinity 18VS variable speed heat pump 25VNA8 (AOC control + inverter)

Likely causes

  • Cooling: Unit heating when cooling is called - reversing valve wiring, AOC fuse or valve problem
  • Coil sensor loose or in the wrong place
  • Outdoor air sensor touching sheet metal or badly placed
  • Outdoor coil blocked

Test and repair steps

  1. Check the fuse on the AOC board and the wiring to the reversing valve; troubleshoot the reversing valve.
  2. Check the coil sensor is clipped to the distributor inlet tube.
  3. Make sure the OAT sensor body is not touching the cabinet.
  4. Inspect the outdoor coil for blockage.

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Source: Carrier 25VNA8 / 24VNA9 Service Manual, Table 6 Fault Code Actions, p.20. Summarized in our own words; check the original manual for your model.

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