B448

Chart:

Schematic:

DESCRIPTION
In the process of controlling the compressor clutch, the Body Control Module (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. If a B447 or B448 is detected, the compressor clutch will disengage and remain disengaged until the diagnostic codes are cleared.

TEST DESCRIPTION
The numbers below refer to circled numbers on the diagnostic chart:
1. BCM input value B1O8 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.

CHART 1A
It has been determined from the previous chart that the problem is not in the low refrigerant pressure switch circuit.

TEST DESCRIPTION
The numbers below refer to circled numbers on CHART 1A:
1. This is a test to determine if the A/C low refrigerant pressure switch opens while the compressor is running. If BIO8 remains "HI" during compressor engagement, then the system fault is due to the refrigerant.
2. This checks if the switch is opening due to a low refrigerant pressure charge or the switch.

Chart: