Climate Control and Scan Tools
Modern automatic climate control systems rely on sensors and actuators to achieve the driver's desired results. Many scan tools can display these input values in datastream. Datastream is great for spotting intermittent problems in A/C systems. They are also capable of bi-directional control. Bi-directional control allows the scan tool to communicate with the control module and actuate components like the compressor clutch, blend door, and blower motor.
The ECT sensor is displayed in volts. The value can be compared to the manufacturer's specifications. An engine coolant temperature sensor or ECT sensor is a variable resistor that uses resistance to change a 5-volt reference signal from the PCM. The sensor's signal changes according to the engine's coolant temperature. It decreases as the engine warms to operating temperature.
Pressure sensors are 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). Modern vehicles have sensors located on both sides of the system. An A/C manifold/gauge and a scan tool can monitor and help diagnose sensor function. Armed with the right scan tool, a technician can monitor system refrigerant pressure without a manifold and gauge set.