B446, B447, B448 Refrigerant System Problem

BCM Code B446, B447, B448:

Low Refrigerant Switch Circuit:

CIRCUIT DESCRIPTION:
In the process of controlling the compressor clutch, the BCM monitors certain system inputs for an indication of low refrigerant charge. If the system refrigerant state of charge should fall below approximately one third its capacity, the BCM is capable of detecting this condition and will display a driver warning message to warn the operator. The BCM determines the state of charge by its low side temperature sensor and the low refrigerant pressure switch. Since temperature and pressure are proportionally related in the A/C system, a low temperature is the same as low pressure. In addition to the message, the BCM will store in memory a diagnostic Code B446, B447 or B448 to indicate that a low refrigerant condition was detected.

Codes B446, B447 and B448 will set under the following conditions:

^ B446 - will set if the low side refrigerant temperature drops too quickly during several compressor cycles.
^ B447 - will set if the low side refrigerant temperature drops much too quickly during several compressor cycles or the low refrigerant pressure switch opens during several compressor cycles.
^ B448 - will set if the low refrigerant pressure switch remains open for several minutes.

TEST DESCRIPTION: Test numbers refer to circled numbers on the diagnostic chart.

1. BCM input value B108 displays the voltage state of the circuit at the BCM.
2. Checks to see if the open circuit reading is due to the circuit or the switch.
3. Checks to see if the fault is on the ignition side or the BCM side of the switch circuit.
4. This step checks to see if the fault is due to the pressure switch or a low refrigerant charge.