HVACopedia

Carrier · Heat pump

55 Outdoor coil temperature sensor fault

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

What the control is telling you

Amber STATUS light flashes 55. The outdoor coil thermistor (OCT) reads open or shorted. Type: Fault; reset: None (fix the sensor).

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

Likely causes

  • Sensor plug not connected to the AOC board
  • Broken or loose harness wire
  • Failed sensor
  • Failed AOC board
  • Sensor not attached, or in the wrong place (must be on the distributor inlet tube)

Test and repair steps

  1. Check the sensor plug is fully seated on the AOC board.
  2. Check the harness for continuity and damage.
  3. Measure sensor resistance and compare with the thermistor table (10K: about 10.0 kohm at 77°F, 32.6 kohm at 32°F).
  4. Replace the sensor if out of range; replace the AOC board only if sensor and harness are good.
  5. Make sure the sensor is clipped to the distributor inlet tube.

Save it for the next call

Star this code in the HVACopedia app and keep the whole library on your phone for jobs with no signal.

Open the app

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.

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.