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Carrier · Air conditioner

74 Discharge temperature lockout

High severity Carrier Infinity 19VS 24VNA9

What the control is telling you

Amber STATUS light flashes 74. Discharge temperature kept going over the limit (elevated from code 59). The unit locks out for 2 hours. Type: System malfunction; reset: 2 hours.

Applies to: Carrier Infinity 19VS variable speed air conditioner 24VNA9 (AOC control + inverter)

Likely causes

  • High load or overcharge
  • Discharge sensor unplugged, wiring broken or sensor failed
  • Indoor airflow too low or off
  • Outdoor airflow too low or off
  • Failed AOC board

Test and repair steps

  1. Cooling check subcooling in Charging Mode (or the subcooling chart on the control box door) and adjust charge.
  2. Check the discharge thermistor (50K about 50 kohm at 77°F) and its harness.
  3. Check indoor and outdoor fans and coils.
  4. Nuisance trips when the unit is not running: see TIC 2015-0017.

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Source: Carrier 25VNA8 / 24VNA9 Service Manual, Table 6 Fault Code Actions, p.22. Summarized in our own words; check the original manual for your model.

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