Circuit Description
WARNING: This page is about a different car, the 2002 Pontiac Grand Prix. However, it is still accessible from the selected car via links, so may be relevant.
Ignition voltage is supplied directly to the A/C compressor clutch relay. The Powertrain Control Module (PCM) controls the relay by grounding the control circuit through an internal solid state device called a driver. The primary function of the driver is to supply the ground for the component being controlled. Each driver has a fault line which is monitored by the PCM. When the PCM is commanding a component ON, the voltage of the control circuit should be near zero volts. When the PCM is commanding the control circuit to a component OFF, the voltage potential of the circuit should be near battery voltage.