BCM Code B448, Low Refrigerant Pressure
In the process of controlling compressor clutch, BCM monitors certain system inputs low refrigerant charge indication. This code indicates a low refrigerant condition was detected. If B448 is detected, compressor clutch will disengage and remain disengaged until diagnostic code is cleared.
NOTE:
Test numbers refer to test numbers on diagnostic chart.
- Checks current state of low pressure switch
- Checks circuits to low pressure switch
- Checks refrigerant system pressure
- Checks restriction in refrigerant system
- Checks intermittent short or open
NOTE:
The table below indicates pressure of Refrigerant-12 (R12) at various temperatures. For instance, a drum of Refrigerant at temperature of 80°F (26.6°C) will have a pressure of 84.1 PSI (579.9 kPa). If it is heated to 125°F (51.6°C), the pressure will increase to 167.5 PSI (1154.9 kPa). It also can be used conversely to determine the temperature at which Refrigerant-12 (R12) boils under various pressures. For example, at a pressure of 30.1 PSI (207.5 kPa), Refrigerant-12 (R12) boils at 32°F (0°C).
TEMPERATURE PRESSURE RELATIONSHIP - R12
| °F (°C) | PSIG (kPa) |
|---|---|
| -21.7 (-29.8) | 0 |
| -20 (-28.8) | 2.4 (16.5) |
| -10 (-23.3) | 4.5 (31.0) |
| -5 (-20.5) | 6.8 (46.9) |
| 0 (-17.7) | 9.2 (63.4) |
| 5 (-15.0) | 11.8 (81.4) |
| 10 (-12.2) | 14.7 (101.4) |
| 15 (-9.4) | 17.7 (122.0) |
| 20 (-6.6) | 21.1 (145.5) |
| 25 (-3.8) | 24.6 (169.6) |
| 30 (-1.1) | 28.5 (196.5) |
| 32 (0) | 30.1 (207.5) |
| 35 (1.6) | 32.6 (224.8) |
| 40 (4.4) | 37.0 (255.1) |
| 45 (7.2) | 41.7 (287.5) |
| 50 (10.0) | 46.7 (322.0) |
| 55 (12.7) | 52.0 (358.5) |
| 60 (15.5) | 57.7 (397.8) |
| 65 (18.3) | 63.7 (439.2) |
| 70 (21.1) | 70.1 (482.7) |
| 75 (23.8) | 76.9 (530.2) |
| 80 (26.6) | 84.1 (579.9) |
| 85 (29.4) | 91.7 (632.3) |
| 90 (32.2) | 99.6 (686.7) |
| 95 (35.0) | 108.1 (745.3) |
| 100 (37.7) | 116.9 (806.0) |
| 105 (40.5) | 126.2 (870.2) |
| 110 (43.3) | 136.0 (937.7) |
| 115 (46.1) | 146.5 (1010.1) |
| 120 (48.8) | 157.1 (1083.2) |
| 125 (51.6) | 167.5 (1154.9) |
| 130 (54.4) | 179.0 (1234.2) |
| 140 (60.0) | 204.5 (1410.0) |