B1347

CIRCUIT DESCRIPTION
In the process of controlling the compressor clutch, the Air Conditioning Programmer (ACM) monitors certain inputs for an indication of low refrigerant charge. If the system refrigerant state of charge should fall below approximately one third its capacity, the ACM is capable of detecting this condition and will display "VERY LOW REFRIGERANT - A/C COMPRESSOR OFF" on the Driver Information Center (DIC) to warn the operator.

The ACM determines the state of charge by monitoring the temperature change in the low side temperature sensor during the initial moments of compressor engagement. This temperature drop is referenced in a table in the ACM as a function of outside air temperature. If the refrigerant charge is too low, the refrigerant boils instantaneously after it passes through the orifice tube, creating a large rapid change in the low side temperature sensor reading. If the temperature change is too great, a very low refrigerant counter is incremented in the ACM. After several incidents have been counted, the ACM will set DTC B1347 and the message "VERY LOW REFRIGERANT - A/C COMPRESSOR OFF" will be displayed on the DIC. If a DTC B1347 is set, the compressor clutch will disengage and remain disengaged until DTC B1347 is cleared.

FAILURE CONDITION(S)
1. Low side refrigerant temperature drops too quickly during several compressor cycles.

ACTION TAKEN
1. Disables A/C compressor until DTC is cleared.
2. Displays "VERY LOW REFRIGERANT - A/C COMPRESSOR OFF" message on DIC.

TEST DESCRIPTION
1. Checks for intermittent open or short in pressure switch circuit.
2. Checks for restrictions in the refrigerant system.
3. An offset in the ACM temperature sensors (actual outside or low side) may cause the triggering of a false DTC. After a long cold soak (preferably overnight) in a shaded cool environment, enter diagnostic without starting engine. All the listed sensor displays should be within 2°C of each other.
4. Recover and recharge system.