A/C Pressure Sensors
Pressure sensors have three wires leading to the control module. This could be the (ECC) Electronic Climate Control, (PCM) Powertrain Control Module or the (BCM) Body Control Module. They’re different from simple two wire pressure switches that have only two states, either open or closed. Like so many automotive sensors, pressure sensors contain three circuits; a 5 volt reference circuit, a signal circuit, and a ground circuit.
They're pressure transducers that convert refrigerant pressure to a variable voltage signal, somewhere between 0.1 V for low pressure (~0 psig) and 4.9 V for high pressure (~430 psig). On some vehicles these sensors are located on both sides of the system. Use a known good manifold and gauge set and a scan tool to diagnose sensor function. Armed with a scan tool a technician can monitor system refrigerant pressure without a manifold and gauge set.