Automatic Air Conditioner
TEST PLAN FOR AUTOMATIC AIR CONDITIONER M 563This section is a brief description of troubleshooting procedures for the electrical system of the air conditioner in Type 928 cars since 1984 model.
We recommend a digital multimeter (e. g. Fluke 75) and a test lamp for testing. Always make sure that the tester is connected on the correct connections for a pertinent test and be conscious of which section of the circuit and which potentials are being checked. Always use a valid wiring diagram for all tests, since this troubleshooting plan only points out the location of components. Comprehensive tests must be made analog the wiring diagram. Information on CEL plug connections and relay designations are in reference to the 1985 on models (with new CEL). All other information is identical.
CHECKING FUNCTION OF ENTIRE REGULATION
It is recommended to check the function of the air conditioner to find a fault, i.e. to find the point where a fault is assumed to be. Deviations from nominal function specifications will normally indicate the faulty circuit or component for initial testing.
Fundamentally
If the air conditioner is without power or vacuum supply, the defroster flap will be open and the circulating air flap set to fresh air and the heater valve will also be open. All other flaps will be closed.
Nominal Functions
A) SENSOR CIRCUIT
Turn on ignition.
Set program switch to DASH
Set temperature switch to 24.
The temperature mixing flap control unit operating motor is mounted on the left side (right side for RHD) of the air guide housing and operates the mixing flaps by way of a lever and linkage. The position of the operating motor can be felt with a finger between the operating motor and air guide housing.
Now move the temperature switch slowly in direction of 18 - the operating motor lever must move down (cooling) at the same speed. In position 18 the lever should be all the way down (max. cooling).
Now move the temperature switch slowly toward 30.
The lever must also move slowly upwards (heating).
At position 30 the lever must be all the way up.
There is a fault in the sensor circuit or operating motor, if there is no step-by-step regulation.
The sensor circuit comprises the outside sensor, inside sensor, control switch and control unit operating motor.
See test point 1. Test Point 1 - Sensor Circuit (Ohmmeter)
B) COMPRESSOR MAGNETIC CLUTCH
Turn on ignition.
Set program switch to DASH
Press AC switch - magnetic clutch must be heard (click).
The compressor clutch drive must be evident with the engine running.
The Circuit has a fault, if the compressor clutch is not activated.
This circuit comprises CEL, AC switch, control switch, evaporator temperature switch, low pressure switch and compressor magnetic clutch.
See test point 2. Test Point 2- Compressor Magnetic Clutch
C) BLOWER
Turn on ignition.
Set program switch to DASH, FOOTWELL, BI or WINDSHIELD.
Turn blower speed switch to 1 - 2 - 3 - 4.
The blower must be running at the different speeds in all switch positions.
Turn speed switch to 0.
Set program switch to DEF.
Blower must be running at maximum speed.
There is a fault in the blower circuit, if there is no function or malfunction of the blower.
Blower circuit comprises CEL, blower switch (on control switch), thermo bimetal switch and blower.
See test point 3. Test Point 3 - Blower
D) FLAP CONTROL
Close door and center nozzles manually.
Start and run engine at idle speed.
Set blower switch to speed 4.
Set temperature switch to 18.
Set program switch to DASH, FOOTWELL, BI, WINDSHIELD and DEF one after the other.
Air Distribution in Position:
DASH only via manually opened center nozzle and/or door window nozzles
FOOTWELL to footwell
BI to footwell and windshield
WINDSHIELD to windshield
DEF to windshield (blower must still run at maximum speed when setting blower switch to "0")
Flap operation is accomplished with engine vacuum via electromagnetic switching valves, which are activated by the control switch.
See test point 4. Test Point 4 - Flap Control