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Rheem · Heat pump

L21 Low pressure control lockout

High severity Rheem/Ruud PRL-JEC heat pump (Comfort Control2 ICC)

What the control is telling you

Active protection after repeated LPC trips. Cooling: LPC opened 3 times in one call - hard lockout. Heating: 3 trips within 120 minutes in one call - hard lockout; or 3 trips in one call with outdoor ambient below 5°F - soft lockout that clears by itself once ambient rises above 5°F. Display alternates L and 21.

Applies to: (-)PRL-JEC 2-stage 16 SEER heat pumps: RPRL/UPRL-024JEC, -036JEC, -048JEC, -060JEC

Likely causes

  • Low refrigerant charge
  • Frozen indoor or outdoor coil
  • Dirty indoor coil/filter or indoor blower not running (cooling)
  • Outdoor fan not running (heating)
  • TXV not working correctly

Test and repair steps

  1. If heating and outdoor temperature is below 5°F, wait until it rises above 5°F before further diagnosis (soft lockout clears itself).
  2. Work through the code 21 checks airflow, coil icing, fans, charge, TXV.
  3. Read stored faults press TEST and SW2 together for 1 second (insulated probes); up to 6 faults scroll, newest first.
  4. Reset the ICC after the cause is fixed press TEST for 1 second with an insulated probe (preferred), or cycle 24VAC (pull R or C) or cycle line power.

Settings for these units

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Source: Rheem (-)PRL-JEC Heat Pump Installation Instructions, 12.4 Active Compressor Protection Mode / 12.6 ICC Diagnostic Codes, p.24, 30. 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.