L21 Low pressure control lockout

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

Outdoor unit clearances · Rheem/Ruud PRL-JEC heat pump (Comfort Control2 ICC)

Do not reduce the 60 in. discharge or 24 in. service clearances.

Inlet clearances under 6 in. reduce capacity and efficiency.

Models that show this code

4 models in Rheem/Ruud PRL-JEC heat pump (Comfort Control2 ICC)

Other codes on the same units

• d4 Memory card invalid for device
• d8 Old shared data
• L4 Locked rotor lockout
• L6 Open start circuit lockout
• L7 Open run circuit lockout
• L29 High pressure control lockout
• Flashing c / C / h / H Anti-short-cycle (3 min) or minimum-run (30 s) timer active
• P Compressor protector trip