The ECM/PCM(Engine Control Module) receives pressure signal in the A/C refrigerant high pressure side from the A/C refrigerant pressure sensor. This input indicates how much load the A/C compressor is putting on the engine and is one of the factors used by the ECM/PCM in order to determine the idle air control position for the idle speed. The circuits consist of a 5V reference and a ground, both provided by the ECM/PCM, and a signal from the sensor. The signal is a voltage which is proportional to the A/C pressure from 0 to 5V. Low pressure produces a low voltage signal and high pressure a high-voltage signal.

Checking output signals from A/C pressure sensor under detecting condition, if an signal above 4.668V lasts for more than 10 sec., ECM/PCM sets P0533.

Fig.1) Normal waveforms of A/C pressure sensor during the time from turning on A/C switch to turning off A/C switch.