Automatic Temperature Control (ATC)

CIRCUIT OPERATION
Several fuses supply power for the Automatic Temperature Control (ATC) system. When the ignition switch is in the RUN position, it connects circuit A1 from fuse 8 in the Power Distribution Center (PDC) to circuit A22. Circuit A22 powers circuit F71 through fuse 12 in the junction block. Circuit F71 connects to the ATC module and the recirculation door motor.

Circuit A7 from fuse 15 in the PDC powers circuit F60 through fuse 20 in the junction block. Circuit F60 supplies power to the ATC module.

When the ignition switch is in the START or RUN position, it connects circuit A1 from PDC fuse 8 to circuit A21. Circuit A21 powers circuit F99 through fuse 18 in the PDC. Circuit F99 powers the coil side of the A/C compressor clutch relay.

Circuit A19 from fuse 7 in the PDC connects to the blower power module and to the coil and contact sides of the high speed blower motor relay.

CIRCUIT OPERATION
When the A/C select switch in the Automatic Temperature Control (ATC) control head closes circuit C90 provides the A/C select signal to the Body Control Module (BCM). After receiving the input, the BCM signals the Powertrain Control Module (PCM) on the CCD bus.

The A/C low pressure and high pressure switches are wired in series and connect to ground on circuitZ1. Circuit C3 from the PCM connects to the low pressure switch. Circuit C21 connects the low pressure switch to the high pressure switch. The high pressure switch connects circuit C21 to ground circuit Z1. If the A/C low pressure and high pressure switches are closed, the PCM senses the A/C request signal on circuit C3.

After sensing the A/C request signal, the PCM supplies ground for the coil side of A/C compressor clutch relay on circuit C13. Circuit F99 from fuse 18 in the PDC powers the coil side of the relay.

When the PCM grounds the A/C compressor clutch relay, the contacts close and connects circuit F25O from fuse 21 in the PDC to circuit C2. Circuit C2 supplies power to the case grounded A/C compressor clutch.

The A/C compressor clutch has a built-in diode. The diode controls the induced voltage that results from the magnetic field collapsing when the clutch disengages. The diode provides a current path to protect other components and systems.