Remove center console right side trim panel. Disconnect 4-pin flat male plug (5}.
Connect term. 1 and 2 (each yellow) to ohiraneter (measuring range x 100, calibrated).
Tester should show the following values.
At 68° F = 2570 ohms ) Blow through sensor housing
) heating of sensor.
If there is no reading or no change in resistance, replace the sensor. Repeat test prior to installing a new sensor.
a) Checking Blower
Connect plug (5) again.
Turn ignition on, set program control optionally to ECO/AUTOM/BI or DEF.
Sensor blower should be running!
Place strip of paper at intake opening or blow cigarette smoke against intake opening. If paper strip is not held or smoke not drawn in, check whether blower is running or whether hose to sensor housing is connected or whether a wire has a break or whether power supply has failed.
3.) Exterior Sensor
The exterior sensor is located at front left in cooling air hose to the alternator. The electric connection is made with a plug in the left headlight well via a further 4-pin flat male plug (4) underneath the center console on right side.
Remove right side trim panel of center console. Disconnect 4-pin plug (4) (one plug is only fitted with three pins).
Connect term. 3 (yellow) and term. 4 (yellow) (on 4-pin plug) with ohmmeter (measuring range x 10, calibrated).
Tester should show the following values.
At 32°F = 933 ohms ) To cause a change in resistance,
) the dooling air hose can be taken
68°F = 588 ohms ) off of alternator. Blow through
) hose with a hot air fan - measured
If the specified values are not reached, repeat test on sensor itself (plug in headlight well).
If measured value is O.K. at sensor, repair wiring to sensor.
4.) Temperature Adjusting Potentiometer in Control Switch
In the control switch there is a potentiometer, which is set by the temperature selector lever. The potentiometer can be adjusted to a specified value.
Remove center console left and right side trim panels. Disconnect 4-pin plug (5). Connect term. 1 (yellow) with ohmmeter (measuring range x 10, calibrated).
Pull off plug (S2) on control unit and connect plug term. 12 (blue) with ohmmeter.
Set temperature control lever to 75° F and read resistance value.
Specification: 1264 - 100 ohms Set temperature control lever to 65° F - reading:
760 - 100 ohms. Set temperature control lever to 85° F - reading:
It is important that the resistance value changes by 500 ohms each time.
If the specified value is not reached or there is no change in resistance at 65 - 85 - 65° F, remove control switch.
a) Removing Control Switch
Lift cover off center console. Unscrew indicator^ plate screws and pull out indicator. (Wires remain connected.) Unscrew the 4 control switch mounting screws and pull out control switch. Pull off plugs on control switch (Bl) and (B2) as well as blower plug.
Connect ohmmeter on the large connector (B2) (left) to platinum terminals 10 and 11. (These are the 4th and 5th platinum terminals from the blower plug'connection.) Repeat test as above.
Remove upper cover of switch (unscrew 2 screws and open clamps on housing edge). A toothed segment, which is mounted on the lever with one screw, can be seen. Set temperature control lever to 75° F. Unscrew toothed segment screw, connect ohmme'ter, turn toothed segment until tester shows 1264 ± 100 ohms.
Tighten screw .and repeat test in 75°°F position. Check for ± 500 ohm change for 6 5 and 85° F positions of temperature control lever.
C.) Control Unit/Flap Operation
The control unit is mounted left on the air box and has 2 electric plugs (SI) and (S2).
The control unit houses an electronic control for regulation of the solenoid valves as well as a servo motor for the temperature mixing flaps.
The control unit can be checked with the control lever or by alternately unplugging and bridging the plug to the inside temperature sensor with the control lever at 75° F.
1.) Checking Power Motor
Turn ignition on and set selector lever to ECO, AUTOM, or 51.
The temperature selector lever has microswitches at 65° F and 85° F end positions, which are closed in these positions and short circuit the control potentiometer. This means that in pos. 6 5°F air conditioner provides max. cooling and in pos. 85° F max. heating. In 65° F position the power motor of the control unit must run to its lowest position (cooling) and at 85° F to its highest position (heating).
The position of the temperature mixing flaps can be checked through the center vent in the heating position. They should be opened fully.
If servo motor is not running, check plug' (S2) term. 3 and 11 for voltage. If sensor circuit is okay, then replace control unit.
Note: The microswitch for 85° F pos. (max. heating) is only standard after about April 1, 19 80.
2.) Checking Activation of Solenoid Valves (Test Lamp)
To be able to check the activation of solenoid valves, it is recommended to remove the control switch and center console side trim panels (see point B 4a).
Connect test lamp to body ground (don't use solenoid valve retaining bar). Hold test light point on wire connector to be tested.
Turn ignition on; move center vent switch down. Testing Sequence
Valve Pos. from left to right
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