While older editions of "Basic Refrigeration and Air Conditioning By P.N." discussed CFCs (R-12) and HCFCs (R-22), modern revisions address the shift to and the new HFOs (R-1234yf) .
| Symptom | Suction Pressure | Discharge Pressure | Likely Cause (Per P.N.) | | :--- | :--- | :--- | :--- | | | Too Low | Too Low | Low air flow over evaporator OR low charge | | Hot compressor, no cooling | Too High | Too High | Overcharge of refrigerant OR non-condensables (air) | | Ice on condenser only | Normal | Very High | Condenser fan motor failed | | Vacuum on low side | Negative | Low | Restriction (clogged filter-drier or expansion valve) |
According to P.N.'s framework, the first truth every student must accept is: Basic Refrigeration And Air Conditioning By P.n.