What It Means
Low pressure safety switch open.
Rheem AC & Heat Pump
Rheem AC & Heat Pump Error Code 21
Troubleshooting guide for the Rheem AC & Heat Pump system fault 21.
Possible Causes
- Low refrigerant charge or leak.
- Frozen indoor evaporator coil.
- Restricted indoor airflow or dirty filter.
- Metering device (TXV) failure.
- Faulty low pressure switch.
Not sure which one it is — or if it's none of these? Try ACLogics today.
Disclaimer: This information is for general reference. Error codes can vary by model and production year. Always refer to your machine's specific manual and the information printed on the unit itself.
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Full Diagnosis
Low pressure control open.
All Recorded Causes
Low refrigerant charge, refrigerant leak, frozen indoor coil, dirty filter, restricted airflow, blocked ducts, expansion device issue, or faulty low-pressure control.
Verify Before Replacing Parts
- Confirm the exact Rheem model family and ac and heat pump context before acting on a generic code description.
- Verify airflow first, then confirm operating pressures and temperature relationship before adjusting charge, since low refrigerant charge, refrigerant leak, frozen indoor coil, dirty filter, restricted air….
- Look for restrictions, iced coils, or dirty heat-transfer surfaces that can mimic a charge problem, and separately confirm the next candidate on the list.
- After the correction, run the system long enough to confirm the ac and heat pump fault does not return under normal load.
Not sure which system this Rheem code is on?
ACLogics has guided diagnostics for 57 Rheem fault codes and asks the right questions to narrow it down.
