System Controls

The ATC Module:

• is fully addressable with the DRBIII®.
• communicates on the Programmable Communication Interface Multiplex System (PCI) Bus.
• broadcasts an A/C request on the PCI Bus to the Powertrain Control Module (PCM) when compressor operation is desired.
• uses input from the evaporator temperature sensor to prevent evaporator freeze up while maintaining optimum cooling performance.
• has dual-zone temperature-controls to provide a wide side-to-side variation in temperature to meet the needs of the driver and the front seat passenger.
• has dual infrared (I/R) sensors mounted in the ATC Module's face which independently measure surface temperature to maintain occupant comfort levels.
• can be operated in a manual mode.
• broadcasts an EBL relay on request on the PCI Bus to the Integrated Power Module (IPM) when EBL operation is desired.
• broadcasts a Blower Relay on request on the PCI Bus to the Integrated Power Module (IPM) at power up.
• controls front blower operating speed, providing 6 blower speeds in manual mode and infinite blower speeds in automatic mode.
• provides a blower delay function for cold engine blower lock out.
  • A Blower Speed Clamping feature minimizes occupant discomfort by controlling the amount of warm air coming out of the HVAC system should the Powertrain Control Module (PCM) disable A/C compressor operation while the Automatic Temperature Control (ATC) is set in an automatic mode. The PCM disables the A/C compressor if the A/C pressure is too low, if the A/C pressure is too high, if engine overheating is immanent, or if an engine overheating condition exists. The ATC clamps the blower speed if the outside air temperature is greater than 50°F (10°C) and the PCM has disabled the A/C compressor. This means that the ATC will not adjust blower speed automatically when the clamping feature is enabled, e.g. if the clamping feature is enabled while in Auto Lo the blower will continue to run in low speed; if the clamping feature is enabled while in Auto Lo and the operator selects Auto Hi the blower will continue to run in low speed; if the clamping feature is enabled while in Auto Hi the blower will continue to run at the highest speed. In any case the operator can manually change the blower speed as desired. When diagnosing blower related symptoms verify that none of the above conditions for disabling the A/C compressor exist before diagnosing the blower circuits and components.
• controls rear booster fan operating speed in automatic mode, providing infinite fan speeds.
• activates and deactivates the Rear Booster Fan Rear Control Switch.
  • The separate Front Blower Power Module and Rear Booster Fan Power Module operate as follows: When blower operation is desired, the power module provides a 12.0 volt signal to the ATC Module via a control circuit. The ATC Module provides a variable duty cycle ground to the 12.0-volt signal based on input from the blower switch. When the blower speed is set to low, the ATC Module provides a short duty cycle (less time grounding the signal voltage). As higher blower speeds are requested, the ATC Module increases the duty cycle (more time grounding the signal voltage). When the highest blower speed is requested, the duty cycle increases to where the signal pattern is almost a flat line (with brief voltage spikes).
• provides a blower after run feature.
  • The blower after run feature evacuates the HVAC evaporator of condensate to prevent odor. This feature operates the front blower motor at a minimal speed for no more than three minutes during a two-hour period after the ignition is turned off. The after run feature will only operate if the A/C system has been on for a minimal amount of time, and ambient air temperature and vehicle voltage are within a specific range.
• controls the electric door actuators' operation.
  • A simplified control system for operation of the front mode, recirculation, and temperature control actuators provides positive positioning without the complexity of feedback from position sensors. The ATC Module knows the number of operating actuator revolutions required for full door travel as well as the number of actuator commutator pulses per revolution. Using these parameters, the ATC Module runs the actuator for the number of commutator pulses that correspond to the desired door position. To maintain accuracy, the system recalibrates itself periodically at known zero and full travel conditions.
  • When a mode change is requested through the MODE switch, the ATC drives the Rear Mode Door Actuator for 10 seconds. The Panel and the Floor/Mix/Defrost mode settings direct rear air flow to the rear panel or rear floor air outlets respectively. There is no Bi-Level position for the rear mode door. When the MODE switch setting is changed to Bi-Level, the rear mode door remains in the last known position (panel or floor). Unlike the front door actuators, the Automatic Temperature Control will not set Diagnostic Trouble Codes for faults pertaining to the Rear Mode Door or its electrical circuits.
• uses Ambient Temperature Sensor data received from the PCI Bus to display outside temperature.
  • This signal is filtered to compensate for hot engine heating effects which can cause erroneous temperature display values.

The Rear Booster Fan Rear Control Switch:

• provides desired rear booster fan speed input to the ATC Module.

The Dual-Zone ATC system uses:

• two, two-wire electric blend door actuators.
• one, two-wire electric front mode door actuator.
• one, two-wire electric recirculation door actuator.
• one, two-wire electric rear mode door actuator.

System Relays

• The Integrated Power Module (IPM) houses and provides power to the A/C Clutch Relay, EBL Relay, Front Blower Motor Relay, and Rear Booster Fan Relay.

Ambient Temperature Sensor

• The ambient air temperature is monitored by the NGC and displayed by the ATC. The NGC receives a hardwire input from the ambient temperature sensor (ATS). The ATS is a variable resistor that operates on a 5-volt reference signal circuit hardwired from the NGC. The resistance in the ATS changes as the outside temperature rises or falls. The NGC senses the change in reference voltage through the ATS resistor. Based on the resistance of the ATS, the NGC is programmed to correspond to a specific temperature. The NGC stores and filters the ambient temperature data and transmits this data to the ATC via the PCI Bus. The ATS cannot be adjusted or repaired and, if faulty or damaged, it must be replaced.