Concorde V6-215 3.5L SOHC (1996)
to determine control for actuators and the blower motor. The BCM interfaces with the ATC display head over the CCD bus. Information on button
activation, blower setting, and temperature setting are supplied to the BCM.
In turn, the BCM supplies the ATC display head with mode information and indication lamp status. The BCM controls blower motor speed by providing
a varying duty cycle of a fixed frequency output (pulse width modulation). There are 14 distinct blower speeds, plus a blower off signal. The body
control module also controls the HVAC mode, temp, and recirculation doors.
ATC Blend, Mode, and Recirculation Door Operation
The DRB trouble codes that indicate a stall failure or a feedback signal failure work together to show what is wrong with the ATC system.
The stall trouble codes mean that the body control module cannot force an actuator to the end of the ATC-heater unit door. Internal problems in the body
control module will set other short-related trouble codes. Having only stall trouble codes indicates that there is a problem with an open or short circuit in
the wiring, a bad actuator, a bad ATC-heater unit door or connecting linkage. It is important that the operation of the ATC-heater unit door be checked if
an actuator is removed. This can be checked by rotating each unit door shaft to confirm that the door will stop at both ends of travel. The actuator itself
has no stops. It must have the ATC-heater unit door to stop travel to pass the stall test.
A feedback signal failure can occur on the blend or mode door. The body control module monitors the feedback signal to check the position of the
actuator. The body control module not only checks the level of the signal but also how much the voltage changes.
A feedback failure can occur if there is a short or open circuit in the wiring, a bad actuator, a bad body control module, a bad ATC-heater unit door or
connecting linkage. The easiest way to diagnose this is to use the DRB to actuate the blend or mode door. Note that the feedback voltage of the actuator
should smoothly change as the actuator is moved. A sudden change in the feedback voltage to a 5.0-volt or a 0.0-volt level indicates the actuator is bad.
A fixed feedback voltage that is less than 5.0 volts or greater than 0.0 volts without a stall failure, or a short failure indicates that the actuator, the
ATC-heater unit door, or a connecting mechanical linkage is jammed preventing movement.
A feedback signal voltage that stays on 5.0 volts or 0.0 volts indicates a wiring or body control module problem.
The feedback failure trouble code can also occur from a lack of actuator travel. This can be checked by confirming that the feedback signal smoothly
changes when the actuator is moved with the DRB. If the signal is OK, the door travel is not correct. The actuator must be removed and the ATC-heater
unit door mechanically checked for proper operation. Typical problems that prevent door movement include screws dropped in the ATC-heater unit or
warped doors. Replace any part that is found defective.
Thermal or Mechanical Problems Affecting ATC Operation
There are several thermal and mechanical problems that can prevent the ATC system from properly controlling the interior comfort of the vehicle. Refer
to the following list of the most common symptoms and possible causes.
1. The system works fine at night but does not seem to properly control temperatures in partly sunny weather (sun intensity changes). The sun sensor
circuit that has failed open or an improperly installed instrument panel top cover will cause this problem. The body control module cannot detect a
sun sensor or wiring that has an open circuit and no trouble code will be recorded. A sun sensor should have a resistance of 1 to 5 mega ohms. The
instrument top cover can block the sun sensor if it covers too much of the sensor. The top cover when properly installed should allow the sun
sensor to stick out 0.25 inch (measured from the top of the sensor to the cover). Refer to the ATC diagnostics in this manual for repair procedures.
Note that items left on the instrument panel that cover the sun sensor can also affect the operation of the system. Refer to the owners manual for
proper operation.
2. The system seems to cycle the interior temperature too hot or cold (erratic temperature control). This problem can be caused when the in-car
temperature sensor does not sense the temperature of the passenger compartment. This occurs when the in-car temperature sensor aspirator motor
does not operate or if certain instrument panel seals are not properly installed. This problem is more noticeable when the weather is very cold or
hot. Small air leaks of cold or hot air from areas other than the in-car temperature sensor inlet (located behind the name plate) will make the sensor
measure the wrong temperature. Refer to Test 9A to diagnose the in-car temperature sensor.
3. The ATC control panel blue display goes blank and the ATC control operates like a manual NC-heater control. This will occur if there is a
problem with the in-car temperature sensor thermistor or vehicle wiring. Note that an in-car temperature sensor trouble code will be present. Refer
to the in-car temperature sensor diagnostics Test 9A in this manual for repair.
4. The system does not seem to cool the vehicle. This can occur if the ATC-heater unit temperature door is not properly calibrated. Start the engine
and perform the ATC-heater unit door calibration with the DRB. Also check the performance of the ATC-heater unit by performing a partial
charge check with the DRB.
5. The panel outlet temperatures seem to cycle. Use the DRB to position the temperature door at a fixed position. If the panel outlet air does not
cycle, refer to the in-car temperature sensor and ambient sensor diagnostics sections in this manual. If the outlet temperature continues to cycle
excessively, check the operation of the evaporator sensor and the A/C system expansion valve (TXV).
6. The air that leaves the ATC-heater unit does not correspond to what the LEDs indicate on the ATC display. Check to see of the ATC control has a
communications trouble code, and refer to diagnostics in this manual. If no trouble code is present, check the operation of the ATC-heater mode
