B446

Code B446 & B447:

Temperature And Pressure Sensor Circuit:

A/C Temperature /Pressure Relationship:

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 monitoring the temperature change in the low side temperature sensor during initial moments of each compressor engagement. This temperature drop is referenced in a table in the BCM as a function of outside air temperature. If the refrigerant charge is too low, the refrigerant will boil instantaneously after it passes through the orifice tube, creating a rapid large change in the low side temperature reading. If the temperature change is too great, a low and/or very low refrigerant counter is incremented in the BCM. Once the counter has reached a calibration value, a low (B446) or very low (B447) refrigerant level is determined and displayed to the owner. If a B447 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. Check for intermittent open or short in pressure switch circuit.

2. Checks for restriction causing intermittent low pressure condition.

3. Checks for restriction within the refrigerant system.

4. An offset in the BCM temperature sensors BD26. Actual outside or BD28 low side may cause the triggering of a false code. After a long cold soak (perferably overnight) in a shaded, cool environment, enter diagnostic s without starting the engine. All the listed sensor readings should agree with 2°C.