Automatic Climate Control

Introduction To ACC

Saab 9000 models sold in the United Stateshave used two basic climate control systems.For identification purposes in this book we willrefer to them as ACC 1 (1986-1989) and ACC 2(1990 onward).

The basic construction and principles of opera-tion for the two systems are very similar butthere are some significant differences, particu-larly in the area of diagnostics. We will highlightthese differences on the following pages.

Both systems measure:l Outside (ambient) temperaturel Inside air temperaturel Mixed air temperature after the heater core0 Sun intensity

This information is combined with input from thedriver and used by the ACC microprocessor tocontrol:

l The AC compressor

l Cabin fan speed

l Air distribution

l Mixed air temperature

l The A.C. air recirculation flap

l Rear window and mirror defrosters

l Rear side window fans (ACC 2 only)

Automatic Climate Control

ACC Unit And Associated ComDonentsm-

ACC 2 ACC 1

1. Automatic climate control unit 4. Indoor temperature sensor

2. Solar sensor

3. Outside temperature indication

ACC I - Sensor located on blower motorhousing

ACC II - Temperature signal received fromEDU

5. Rear door fans

6. Rear window heater

7. Outside mirror heaters

Automatic Climate Control

ACC Unit And Associated Components

12. Ventilation fan motor

Automatic Climate Control

Inputs

The temperature indication signals from the in-door and mixed air temperature sensors are DCsignals proportional to temperature. Power issent to the indoor temperature sensor for asmall fan which moves air through the sensor.

On ACC I the outside temperature signal is cal-culated via voltage drop across a PTC resistormounted on the main blower motor housing.

On ACC 2 the EDU orocesses a signal from the,~ --~sensor mounted below the front bumper, con-verts it to digital pulses and transmits it to theACC.

On ACC II, the solar sensor input is also an out-put since it is a serial data link providing 2-waycommunication between the microprocessorsused in the solar sensor and ACC unit.

The battery +30 supply provides the main powerfor the unit and the +54 ignition supply is used

The rheostat supply is used for the push button

to switch on the unit.lamps and during darker conditions also suppliesthe LED indicators.

The AC output and the output to the rear windowand mirror heater are 12V signals to operaterelavs.

ACC 2 - A pulsed power signal to operate thestepper motors. By counting the num-ber of oulses the ECU can determineflap position.

On ACC II, the ISAT output and input providesthe communication between the ACC and ISAT Air distribution flapmicroprocessors.

The remaining outputs are all motor drives asfollows:

@ICC 1 Reversible DC motor with a built in vari-able resistor to feedback door positioninformation to the ECU

Ventilation fan: Variable 0 to 5V DC signal tothe fan speed controller. The fan feedback sig-nal is a 1 to 12V DC signal proportional to thespeed of the fan.

?ACC 2 A pulsed power signal to operate thestepper motors. By counting the num-ber of pulses the ECU can determineflap position.

Air recirculation flap: Reversible constantspeed DC drive. Rear door fans

Temperature control flap ACC 2 - Variable voltage supply from 7-11 VDCproportional to cabin blower Speed

ACC 1 - Reversible DC motor with a built in vari-abl8 resistor to feedback door positioninformation to the ECU

ACC 1 - Not controlled by ACC, two speedrocker switch on the console.

Automatic Climate ControlRecirculatjon Flap And AC Unit

Depending on the position of the recirculationflap, ventilation air from the passenger compart-ment is either recirculated or fresh air is drawnin from outside, providing outside conditions per-mit.

After the recirulation flap the air passes throughthe evaporator to the cabin fan.

Auto modeFor the first 60 seconds after staring, the recir-culation flap remains in the fresh air position.

With an outside temperature of 81’ F (27O C)or more the flap is in the recirculation posi-tion.With an outside temperature of 79” F (26’ C)or less the flap is in the fresh air position.

Automatic Climate Control

Ventilation Fan, Temp. Control & Air Dist. Flapsm

The fan is located after the evaporator andblows air to the temperature control flap whichdetermines the amount of air that passes overthe heater; in the 0% flap position no air flowsover the heater and in the 100% position all theair is heated.

The air distribution flap is at the end of the airflow path and routes the air to the required ar-eas of the car. The positions of this flap can beselected either manually or automatically.

Automatic Climate Control

ACC Unit And Power Supplies

The unit is powered from the +54 and +30 cir-cuits.

Indicators on the unit consist of a 2-digit displayof the selected temperature and LEDs to indi-cate AUTO and/or the current manual selections.The 2-digit display is also used to indicate thenumber of faults, if any, which may be detectedby the self test program. On ACC II units, thenumber of faults will be automatically shown onthe display for approximately 10 seconds afterstarting.

On ACC II, the LEDs and display are powered by

a pulsed supply. In dark conditions the illumina-tion level is controlled by the rheostat and inbright conditions by the ACC unit. The illumina-tion is measured by a photo-transistor on theACC panel.

On ACC I, backlighting for the push buttons isprovided by 3 bulbs powered by the rheostat.

On ACC II, backlighting for the push buttons isfrom four bulbs powered by the rheostat. Togain access to the lamps, remove the front cov-er.

Automatic Climate Control

Temperature Sensors - ACC 1

The ACC system needs three different tempera-ture inputs to operate. This data is provided bythe following solid state resistors:

l Inside Temperature - A small fan draws airthrough the small vent to the right of the instru-ment cluster, ensuring an accurate samplingof cabin temperature.

l Mixed Air Temperature - This NTC measuresair temperature downstream of the evaporatorand heater core before it enters the distributionducts.

l Ambient Temperature - Outside (ambient) airtemperature is measured by a PTC (PositiveTemperature Coefficient) sensor mounted onthe outside of the cabin blower fan housing.In this position it samples the air being drawninto the evaporator housing.

Automatic Climate ControlFlap Position Motors - ACC 1

The temperature control and air distribution flapsfor the ACC I system are controlled by a sealeddrive unit consisting of the following compo-nents:

l A reversible high speed DC motor

l A multistage gear reduction

l A variable resistor allowing the ACC ECUto sense output shaft position.

The variable resistor is preset during assemblybut may become out of sync if proper proce-dures are not followed when servicing the dash.Erratic operation of the ACC, normally accompa-nied by a fault code on the diagnostic displaywill be the result.

There is no easy way to reset the resistor, therecommended repair is to replace the unit.

To avoid damage always follow these guidelines:

l Never power up an unmounted motor. Themounting hardware limits shaft rotation pre-venting you from overrunning the stops onthe variable resistor.

l Before removing the drive assembly selectHI on the temperature display.

l Allow the system to operate briefly until theflaps have locked in position, then turn thecar off and remove the negative batterycable.

Automatic Climate Control

Recirculation Flap Motor--mzj-

This is a fixed speed DC motor which runs inforward or reverse to move the flap between thefresh air and recirculation positions under controlof the ACC unit. After approximately 15 sec-onds, the motor will switch off automatically.

Automatic Climate Control-Solar Sensors

ACC 1

The solar sensor on cars equipped with ACC I is

tensity of the sun. This information allows theECU to modify cabin fan speed as a means of

a photo cell which reacts to changes in the in-

compensating for the affects of sun loading,This can be a significant factor considering thelarge areas of glass common in todays cars.

In the ACC II system the solar sensor is a micro-processor based unit fitted above the dash tosense the solar energy through the windshield.It consists of five solar cells and a microproces-sor. The microprocessor transmits digital signals

The sensor is enclozd in a scratch-proof cover

to indicate the intensity, angle of elevation and

constructed of extremely tough epoxy-coatedplastic. The top of the cover also acts as a fil-ter, allowing only infra-red radiation to penetrate.

bearing of the sun.q_&c

The sensor is soldered into the printed circuitboard which in turn is fitted in a plastic box andfilled with silicone.

The message indicating the three measure-merits, unit is transmitted to the ACC unit in se-rial form at l-second intervals.

Automatic Climate Control

Air Conditioning Unitm-

The air conditioning system consists of a com-pressor, evaporator and condenser. An anti-frost switch is fitted on the evaporator and highand low pressure limit switches are fitted on thereceiver dryer which is mounted on top of theevaporator.

Temperature control is achieved by blendingcold air from the evaporator with hot air fromthe heater core.

Automatic Climate Control

Air Conditionina Unit Controlw-

To prevent the AC operating when ECON is se-lected the 12V control signal from the ACC unitis removed.

Other conditions which must be satisfied for theAC unit to operate are:

l When the contacts of both the high and lowpressure switches, located on the receiver dry-er are closed.

l The anti-frost thermostat fitted to the evapora-tor is in the closed position.

l The starter motor is not running.l The engine has been running for at least 10 se-

conds after start.l The engine is not running at full throttle.

To achieve the 10 second delay on earlier mod-els, a timing relay is used. Beginning with LH2.4.1 all interlocks which are dependent on thefuel injection system are incorporated in the LHECU and an ordinary double or nothing relay isused.

To increase condenser cooling if the pressure ofthe refrigeration gas starts to rise, a pressureswitch applies a signal to start the radiator fan.

Automatic Climate Control

Ventilation And Rear Door Fans

The ventilation fan is driven by a variable speedDC motor. The speed is selected automaticallyin the AUTO mode and under control of the fanspeed push buttons in the manual mode. Tocontrol the speed the ACC unit applies a controlsignal to a fan control unit which in turn variesthe motor current. The rate of change of cur-rent is approximately 1 A per second. The cur-rent at maximum speed is approximately 16 A.

unit to monitor the speed of the ventilation fanmotor.

The rear door fans on ACC I cars are controlledby a console mounted switch with HI, LO andOFF positions. Fan speed is controlled by around ceramic resistor mounted under the driv-ers seat.

When HI or LO is selected on the temperatureindicator the motor runs at maximum speed con-tinuously.

The rear door fans on cars with ACC II are alsodriven by variable speed DC motors. They havea preset minimum speed, increase in step withthe ventilation fan in the middle of the range,

On ACC I models (and early M90 ACC II mod- and run at maximum speed at the top of theels), a feedback signal from the negative termi- range. When the rear window heater is switchednal on the ventilation fan motor enables the ACC on, the door fans run at maximum speed.

Automatic Climate Control--~ mg ~

Rear Window And External Mirror Heaters

The +30 supply to the rear window and the ex-ternal mirror heaters is switched on via a relaycontrolled by the ACC unit thereby enablingthese functions to be controlled automaticallywhen required.

On ACC II, when the indoor temperature is lessthan 5O’F (+lO’C) at ignition on, the supply isswitched on automatically for approximately 10

minutes but can be manually switched off beforethis period has expired. Switch off after 10 min-utes also occurs when the heater is switched onmanually.

On ACC I, the 10 minute timing function is iden-tical. The only difference is that the heaters areswitched on when the outdoor temperature isless than 10% at ignition Uon”.

Automatic Climate Control

&otnat!c And Economy Modesm-

In the AUTO and ECON modes the system worksto maintain the temperature at the selected val-ue by controlling the positions of the various airflaps and the speed of the ventilation fan. Thetemperature selection range is 62-82’F (17-27”

C)*

With LO selected the temperature control flap isset to the 0% (bypass heater) position and the

air distribution flap is set to VENT (flap angle 45degrees). No temperature control occurs andthe ventilation fan runs at maximum speed.

With HI selected, the temperature control flap isset to the 100% position (maximum heating) andthe air distribution flap set to the (DEF-HEAT)position. No temperature control occurs and theventilation fan runs at maximum speed.

Automatic Climate Control

Manual Modew-

Manual selection of any of the following condi-tions causes the AUTO indicator to extinguish.

a Air recirculationa Ventilation fan speedl Air distr ibutiona Off mode (ACC II only)a Economy mode

if for example an air distribution button (alreadylit) is pressed, air distribution begins to operatemanually while air recirculation and ventilationfan speed continue to function automatically.The same applies to air recirculation and ventila-

tion fan speed. Auto selection reverts every-thing to auto mode.

When rear window heater u on” or “off” is se-lected manually, the corresponding indicatorlights or extinguishes but the AUTO indicator re-mains lit. Similarly, manual selection of reardoor fans “off” (ACC II only) causes the indica-tor to extinguish but does not affect the AUTOindicator.

When the position of any of the control mecha-nisms is selected manually, the others continueto operate in the automatic mode to maintainthe temperature constant.