System Controls

The ATC Module:

• is fully addressable with the DRBIII®.
• communicates over the Programmable Communication Interface Multiplex System (PCI) Bus.
• provides an A/C request over the PCI Bus to the Powertrain Control Module (PCM) when compressor operation is desired.
• for exports with diesel engines, provides a Cabin Heater activation request over the PCI Bus to the Front Control Module (FCM) when conditions are favorable for Cabin Heater operation.
• uses input from the evaporator temperature sensor to prevent evaporator freeze up while maintaining optimum cooling performance.
• uses input from infrared (I/R) sensors, which measure surface temperature, to maintain occupant comfort levels.
  • The I/R sensors are mounted in the instrument panel center bezel.
• can be operated in a manual mode.
• provides a blower relay on request over the PCI Bus to the Front Control Module (FCM) when blower operation is desired.
• controls front blower operating speed, providing 10 speeds in manual mode and infinite speeds in automatic mode.
• provides a cold engine blower lockout function.
  • 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 blower operating speed, providing 10 speeds in manual mode and infinite speeds in automatic mode.
  • The separate front and rear Blower Motor Controllers operate as follows: When blower operation is desired, the Blower Motor Controller provides a 10.0 volt signal to the ATC Module over a control circuit. The ATC Module provides a variable duty cycle ground to the 10.0 volt signal based on input from the blower switch. When the blower switch is set to LO speed, 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 blower switch reaches HI speed, the duty cycle increases to where the signal pattern is almost a flat line (with brief voltage spikes).
• controls the front and rear electric door actuators' operation.
  • A simplified control system for operation of the 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.
• activates and deactivates the Rear ATC Switch.

The Rear ATC Switch (Three-Zone Only):

• provides desired rear blower speed input to the ATC Module.
• provides desired rear blend and mode door position input to the ATC Module.

The Dual-Zone ATC system uses:

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

The Three-Zone ATC system uses:

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

System Relays

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