Rear A/C Pressure Transducer - Operation

OPERATION

The rear A/C pressure transducer monitors the pressures in the high side of the rear refrigerant system through its connection to the rear liquid line at the rear A/C receiver/drier. The rear A/C pressure transducer will change its internal resistance in response to the pressures it monitors.

The Front Control Module (FCM) provides a five volt reference signal to the rear A/C pressure transducer, then monitors the output voltage of the pressure transducer on a sensor return circuit to determine rear refrigerant system pressure. The FCM broadcasts a rear refrigerant pressure message to the Engine Control Module (ECM), which is programmed to respond to the rear A/C pressure transducer and other sensor inputs by controlling the operation of the rear A/C clutch and the rear condenser cooling fans to help optimize rear A/C system performance and to protect the rear refrigerant system components from damage. The ECM will disengage the rear A/C clutch when high side pressure rises above 3275 kPa (475 psi) and re-engage the clutch when high side pressure drops below 1999 kPa (290 psi). The ECM will also disengage the rear A/C clutch if the high side pressure drops below 193 kPa (28 psi) and will re-engage the clutch when the high side pressure rises above 234 kPa (34 psi). If the rear refrigerant system pressure rises above 1655 kPa (240 psi), the ECM will actuate the rear condenser cooling fans. The rear A/C pressure transducer message to the ECM will also prevent the rear A/C clutch from engaging when ambient temperatures are below about 4.5° C (40° F) due to the pressure/temperature relationship of the refrigerant. See the Electric A/C Condenser Cooling Fan Switch Point chart for condenser cooling fan on/off pressures.

The rear A/C pressure transducer is diagnosed using a scan tool Testing and Inspection.

The rear A/C pressure transducer cannot be adjusted or repaired and must be replaced if inoperative or damaged.

ELECTRIC A/C CONDENSER COOLING FAN SWITCH POINT