What does 21 mean?
Suction pressure dropped below minimum threshold. Refrigerant circuit issue detected.
Common causes
- Low refrigerant charge - possible leak
- Dirty evaporator coil
- Failed TXV or metering device
- Blocked suction line
- Outdoor temperature too cold for operation
Diagnostic & testing steps
- 1. Check suction pressure with manifold gauge set
- 2. Normal suction: 60-80 PSI (R-410A) at 70°F ambient
- 3. Check evaporator coil for ice or heavy dirt buildup
- 4. Inspect TXV or orifice for proper operation
- 5. Check for refrigerant leaks with leak detector
- 6. Verify outdoor temp is above minimum operating range
Tools required
- Manifold gauge set
- Electronic leak detector
- Thermometer
OEM parts & part numbers
TXV Valve, Refrigerant (R-410A), Low Pressure Switch
Part numbers: EF30CW232, HK02AA006
Safety warning
⚠️ REFRIGERANT HAZARD: EPA 608 certification required to handle refrigerant. Never vent refrigerant to atmosphere.
Try DiagBuddy AI free — instant 30-second diagnostics for technicians.