Detailed description

Detailed description

The control module activates the direct current motor until polarity causes the current air mixture setting measured from the motor potentiometer to be the same as the desired air mixture setting.

Air distribution

Set the desired air mixture with the knob on the panel with the following 9 settings:

1.

Panel

2.	Intermediate

3.	Panel + Floor

4.	Intermediate

5.

Defrost

6.	Intermediate

7.	Defrost + Floor

8.	Intermediate

9.

Floor

A direct current motor with built-in potentiometer rotates the air distribution damper via linkage. The air distribution knob is connected to a potentiometer which receives an internal control module voltage feed. The potentiometer applies voltage to the internal control module inlet which increases when the knob is rotated to the right. The A/D value is converted in a control module memory table containing information regarding which air distribution setting (desired) is to be used for a specific A/D value.


The control module activates the direct current motor until polarity causes the current air distribution setting measured from the motor potentiometer to be the same as the desired air distribution setting.

Fan speed

The knob is connected to a potentiometer which is supplied with current internally from the control module. The potentiometer has 6 fixed positions and delivers a voltage to the control module's internal input which increases when the knob is turned clockwise. The value is A/D converted.


A table in the control module memory contains the indicated voltage which is sent to the fan control unit at a specific A/D value. Control voltage is as follows:

Knob setting	0	1	2	3	4	5
Control voltage	0	1.64 V	2.3 V	2.62 V	3.10 V	5 V

When the starter motor is running, a control voltage of 0 V is set despite the knob setting. The MCC detects that the starter motor is running since +54 receives no voltage while +15 receives voltage.

Air recirculation

The button is read by the control module which supplies current to a DC motor that drives the air recirculation flap to the desired setting. The motor is activated for a period of 10 s. An LED indicates that recirculation has been switched on. Fresh air can be selected if the air distribution knob is set to defrost, after which it is possible to select recirculation manually. The MCC stores recirculation status during ignition shut-off if the A/C is switched on and recirculation is active. The status is re-activated when the ignition is switched on.

A/C

When the A/C button is activated, a ground feed is supplied from pin 18 to the ECM. A diode indicates that the function is active. The BCM requests A/C cut-in from the ECM. The MCC stores A/C status when the ignition is switched off and re-activates the same status once the ignition is switched on.

Electrically heated rear window and rear view mirrors

The button is used to switch the rear window defrost on and off. When the button is depressed, a ground pulse is sent from pin 4 to the BCM. When the BCM sends a request for electrically heated rear window cut-in, the BCM will also supply B+ on the MCC unit pin 22 which will light a diode indicating that the function is operating. The REC activates the electrically heated rear window relay. The corresponding door module activates mirror heating.

Parking heater

The parking heater is activated from the ICM via SID and SIDC. The parking heater relay is controlled by the BCM. The relay applies B+ on the MCC unit pin 32 (+54) when the heater is activated. When the ignition is switched of, the following setting is the result:

•	Air mixture 100% heat

•	Air distribution defrost

•	Recirculation in fresh air setting

•	The fan speed is set to match knob position 1, irrespective of the actual setting of the knob

Diagnostics

The system contains no bus connection and does not communicate with the diagnostic tool. No diagnostics exist.

Calibration

The system has no calibration function.