1999-2004 Grand Cherokee models feature either a Manual Temperature Control (MTC) or Automatic Zone Control (AZC). The Automatic control is available only on Limited or Overland models. The manual temperature control HVAC system uses a combination of electrical, and vacuum controls. The Automatic Zone Control HVAC system uses only electrical controls. These controls provide the vehicle operator with a number of setting options to help control the climate and comfort within the vehicle. Refer to the owner’s manual in the vehicle glove box for more information on the suggested operation and use of these controls.

Both a/c heater control panels are located on the instrument panel inboard of the steering column and below the radio. Both control panels contain rotary-type temperature control knob(s), a rotary type mode control switch knob, a rotary-type blower motor speed switch knob and an air conditioning compressor push button switch. The rear window defogger push button switch is also located on a/c heater control panel. The AZC control panel also features a recirculation push button switch and a vacuum fluorescent display area.

AZC operation

The AZC control module uses infrared sensing technology to control occupant comfort levels, not the actual passenger compartment air temperature. Dual infrared sensors mounted in the face of the control unit independently measure the surface temperature to maintain customer-perceived comfort temperature under changing conditions. Dual Zone temperature control provides wide side-to-side variation in comfort temperature to exceed the needs of either front seat occupant. This sensing system replaces interior air temperature and solar sensors used to approximate direct sensing control through complex control programs.

The AZC system:

• Communicates over the Programmable Communication Interface Multiplex System (PCI) Bus.
• Has dual infrared sensors, mounted in the AZC module face, which independently measure surface temperature to maintain occupant comfort levels.
• Has dual-zone temperature-controls to provide a wide side-to-side variation in temperature to meet the needs of either front seat occupant.
• Can be operated in a manual mode.
• Uses engine temperature data, received over the PCI Bus, for cold engine blower lock-out.
• Uses engine RPM data, received over the PCI Bus, for wide-open throttle A/C cut-out.
• Uses vehicle speed data, received over the PCI Bus, to determine air-flow over the condenser for optimum cooling performance.
• Uses Ambient Temperature Sensor data, received over the PCI Bus, to optimize comfort control.
• Provides an A/C request to the BCM when compressor operation is desired.
• Provides a request to the BCM when rear defogger operation is desired.

• Controls fan speed, providing 10 blower speeds in manual mode and infinite speeds in automatic mode.

  The Blower Motor Controller provides a 5.0 volt signal to the AZC Module over the Blower Motor Control circuit. The AZC Module provides a variable duty cycle ground to the 5.0 volt signal based on input from the blower switch. When the blower switch is set to LO speed, the AZC Module provides a short duty cycle (less time grounding the signal voltage). As higher blower speeds are requested, the AZC 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 electronic door actuator 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 AZC 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 AZC 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.

AZC system doors:

• Two, two-wire electronic blend door actuators.
• One, two-wire electronic mode door actuator.
• One, two-wire electronic recirculation door actuator.

System revisons

The 2003-2004 model year AZC Module is NOT interchangeable with 1999-2002 AZC Modules due to revised control software.

AZC fault codes

Fault codes are two-digit numbers that identify a circuit that is malfunctioning. The Automatic Zone Control (AZC) control module has a system self-diagnostic mode which continuously monitors various parameters during normal system operation. If a system fault is detected, a current and historical fault is recorded. When the current fault is cleared, the historical fault remains until reset (manually or automatically). Both the current and historical fault codes can be accessed through either the front panel, or over the Programmable Communications Interface (PCI) bus using a DRBIII scan tool, and the appropriate diagnostic information.

The two different kinds of fault codes are:

1. Current Fault Codes - Current means the fault is present right now. There are two types of current faults: input faults, and system faults.

2. Historical Fault Codes - Historical or stored means that the fault occurred previously, but is not present right now. A majority of historical fault codes are caused by intermittent wire harness or wire harness connector problems.

AZC self-diagnostic mode:

1. To enter the self-diagnostic mode, depress the a/c and recirc buttons at the same time and hold. Rotate the left temperature control knob clockwise (CW) one detent.

2. If you continue to keep the a/c and recirc buttons depressed, the AZC control module will perform a Segment Test of the Vacuum Fluorescent (VF) display. In the Segment Test you should see all of the display segments illuminate as long as both buttons are held. If a display segment fails to illuminate, the vacuum fluorescent display is faulty and the a/c heater control must be replaced.

3. After viewing the Segment Test, release the A/C and Recirc buttons and the display will clear momentarily. If there are no fault codes, the “00” display value will remain in the VF window. Should there be any codes, each will be displayed for one second in ascending numerical sequence (note: no effort is made to display faults in the order they occurred). The left side set temperature display will be blanked and the right side set temperature display will indicate current and historical codes (8 historical max) presently active.

Once all codes have been displayed, the system will repeat the fault code numbers. This will continue until the left side set temperature control is moved at least one detent position in either direction, by pressing both the A/C and Recirc buttons at the same time, or the ignition is turned off. Record all of the fault codes, then see the Current and Historical Fault Code charts below for the descriptions.

Clearing fault codes

Current faults cannot be electronically cleared. Repair must be made to the system to eliminate the fault causing code. Historical fault codes can be cleared manually, or automatically. To clear a historical fault manually, depress and hold either the A/C or Recirc button for at least three seconds while the display is in the fault code mode of operation. Historical fault codes are cleared automatically when the corresponding current fault code has been cleared, and has remained cleared for 72 ignition cycles. The faults have been cleared when two horizontal bars appear in the Test Selector display.

Calibrating AZC door actuators

Calibrate the door actuators after making any repairs to the AZC system. To calibrate the door actuators proceed as follows:

1. Turn the ignition on.
2. Set the AZC to automatic.
3. Turn the ignition off.
4. Remove the IOD fuse from the Power Distribution Center. Wait several seconds, and then install the IOD fuse.
5. Turn the ignition on. Do not touch any of the AZC controls for at least one minute to allow the calibration function to run to completion.

Every 20 key cycles the AZC head initiates a re-calibration routine which identifies pulse counts required to achieve full door travel. Also during this routine all modes and functions are validated as functional. When the self calibration routine is complete, the control head resets itself to its last settings.

The air conditioning compressor will engage in certain modes to cool and remove moisture from air entering the passenger compartment. The AZC control, when it is not set in the auto mode, always defaults to A/C enabled. The LED illuminates when the control requests A/C. The customer must toggle A/C off by depressing the button every time he turns to manual mode or the A/C is enabled. Additionally, when the vehicle is off for a "calibratable" amount of time, automatic A/C is again enabled and the customer must again force it off by depressing the button.

See also  Blower motor

Change in outlet temperature from desired setting - 1999-2001 models (see TSB # 2400701)

Cold air leaking into passenger compartment foot well - 1999-2000 models (see TSB #242599)

Condensation on exterior of heater housing - 1999-2000 models (see TSB #240699A)

Heater A/C system changing to defrost mode when accelerating - 1999-2000 models (see TSB # 242499)

Reduced airflow from center outlets - 1999 models (see TSB # 240799)

Temperature coming from the HVAC system blows cold air only. - Air temperature remains cold regardless of the position of the temperature knob. Observe the temp door actuators on the HVAC housing while rotating the temp knob. If the actuators rotate, but the air temp does not change, the problem could be a broken temp door or temp door stop. Blend doors and doorstops are available through the Mopar Parts. The part number of the doorstop is 05012711AA.

Temperature fluctuation in the automatic mode - 1999 models (see TSB #241699. Involves AZC module recalibration. Also addresses having to set the temperature too high or low to maintain a comfortable passenger compartment, constantly having to adjust the temperature setting when in automatic mode and temperature overshoot in automatic mode).

Water drips onto the passenger floor when air conditioning is on - Ensure the condensation drain is free of restriction. High temperature and humidity will promote condensation buildup on the exterior of the HVAC housing. Self adhesive foam tape is available that will help absorb water droplets that may form on the HVAC housing. Dry the areas where water condensation is the most. Carefully install self adhesive foam tape Part # 05015245AA.

Whistling sound from heater blower - 1999 models (see TSB # 240899)