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Carrier 55: Coil temperature sensor fault

Source: Carrier manual (PDF) (opens in a new tab) ↗ · Updated

Status code55Carrier
What does Carrier 55 mean?

Coil temperature sensor fault.

Homeowner part this code names: AC coil cleaner.

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Call a pro: jump to when to call a pro Equipment type: AC / heat pump
How it shows: Amber status LED on a Carrier Infinity 25VNA8 heat pump or 24VNA9 air conditioner. Short flashes, then long flashes. Code 55 is 5 short flashes and 5 long flashes

Carrier 55 is a coil temperature sensor fault. Count 5 short and 5 long. The manual wants the thermistor clipped to the distributor entry tube, the harness checked, and the outdoor control replaced only if its hardware is damaged. If this sensor fails, defrost runs every interval in heating and stops after 2 minutes. That short defrost is why a heat pump can feel like it is not heating. Code 53 is the outdoor air sensor, which fails over to a different defrost rule.

Likely causes

  • Sensor harness not connected to the AOC control
  • Broken or loose harness wire
  • Coil thermistor not properly attached, or attached in the wrong location
  • Broken or damaged sensor
  • Hardware damage to the AOC control

Safe checks for 55

  1. If the outdoor coil thermistor fails, the manual says defrost occurs at each time interval during heating, and ends after 2 minutes
  2. Technicianmake sure the sensor is clipped to the distributor entry tube, check the harness, and replace the AOC only if its hardware is damaged
Safety firstOutdoor units carry line voltage even when the thermostat is off. Switch off the unit's disconnect and breaker before touching anything. Refrigerant, wiring, compressor and control-board work must be done by a licensed HVAC technician.

Capacitors can hold a charge after the power is off. Safety terms.

When to call a pro

Call a licensed HVAC technician if 55 is flashing. Short defrost cycles in cold weather can be this sensor, not an empty refrigerant charge.

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Parts & tools for this fix

Taken from this code's causes or steps. A search link opens Amazon results and does not confirm a fit. Check the model number in the manual.

AC and heat pump coil cleaning supplies: guide

In this code: Coil thermistor not properly attached, or attached in the wrong location

See the guide for what to look for when buying one.

Related Carrier AC / heat pump codes

48Lost inverter communications (system malfunction)49Compressor overcurrent fault53Outdoor air temperature sensor fault56Outdoor air temperature and outdoor coil57Suction pressure sensor fault65DC volts low, speed limiting

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