Connect Scantool to Data Link Connector (DLC).
Warm engine up to normal operating temperature.
Turn "OFF" electrical devices and A/C.
Monitor " A/C PRESSURE SENSOR " parameter on the scantool.
Specification :
A/C "OFF" : 1200mV~1800mV
A/C "ON" : Higher than A/C "OFF" pressure by more than 500mV
A/C pressure transducer voltage varies too much, therefore do not concern too much about the figure instead, check the rising tendancy of A/C pressure transducer.