Mercedes-Benz ML320. Service manual - part 647

 

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Mercedes-Benz ML320. Service manual - part 647

 

 

Fig. 3: Connecting Test Cable & Socket Box To A/C Push-Button Control Unit 
Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

 

2001 Mercedes-Benz ML320 

2000-01 MANUAL A/C-HEATER SYSTEMS ML 320, ML 430 & ML 55

  

me 

 

FUNCTIONAL TEST PREPARATION 

1. Check condition of fuses F16, F41, F43 and F44. See WIRING DIAGRAMS . Repair and/or replace 

fuses and necessary.  

2. Turn ignition on. Locate in-vehicle temperature sensor aspirator blower vent grille above anti-theft 

indicator light. Place a half-inch square of tissue paper over aspirator blower vent grille. If paper stays on 
vent grille, go to next step. If paper does not stay on vent grille, correct insufficient aspirator blower 
ventilation.  

3. Put shift lever in "P" and engage parking brake. Run engine at idle until it reaches normal operating 

temperature, about 176°F (80°C). Ensure ambient (outside) temperature is greater than 58°F (15°C).  

4. Manually open center and side air outlets. Ensure recirculation button is not depressed. Set blower speed 

knob to position No. 1.  

FUNCTION TEST 

Defrost Mode 

To check operation in defrost mode, set temperature selector knob to White range (vertical). Set mode control 
knob to 12-o'clock position (vertical). Ensure A/C button indicator is illuminated. Air will vent from defrost and 
center outlets and A/C compressor will engage. If operation is not as specified, perform the following in order:  

Check voltage supply circuit Z50/2 between No. 16 fuse (15-amp) and connected components. See 
VOLTAGE SUPPLY CIRCUIT Z50/2 under ELECTRICAL TESTS.  

Check ground circuit. See GROUND CIRCUIT Z50/4 under ELECTRICAL TESTS.  

Check in-vehicle temperature sensor signal voltage. See IN-VEHICLE TEMPERATURE SENSOR 
under ELECTRICAL TESTS.  

Check in-vehicle temperature sensor signal resistance. See IN-VEHICLE TEMPERATURE SENSOR 
under ELECTRICAL TESTS.  

Check icing protection temperature sensor signal voltage. See ICING PROTECTION 
TEMPERATURE SENSOR
 under ELECTRICAL TESTS.  

Check icing protection temperature sensor resistance. See ICING PROTECTION TEMPERATURE 
SENSOR
 under ELECTRICAL TESTS.  

Check activation voltage during temperature reduction. See ACTIVATION VOLTAGE 
TEMPERATURE
 under ELECTRICAL TESTS.  

Check activation voltage during temperature increase. See ACTIVATION VOLTAGE 
TEMPERATURE
 under ELECTRICAL TESTS.  

Check blend air flap actuator motor operation voltage. See BLEND AIR FLAP ACTUATOR MOTOR 
under ELECTRICAL TESTS.  

Check blend air flap actuator motor resistance. See BLEND AIR FLAP ACTUATOR MOTOR under 
ELECTRICAL TESTS.  

Check A/C button activation. See A/C BUTTON under ELECTRICAL TESTS.  

Check A/C pressure switch. See A/C REFRIGERANT PRESSURE SWITCH under ELECTRICAL 

NOTE:

Function test steps must be performed in order given.

 

2001 Mercedes-Benz ML320 

2000-01 MANUAL A/C-HEATER SYSTEMS ML 320, ML 430 & ML 55

  

me 

 

TESTS.  

Normal Ventilation In Regulating Mode 

To check normal ventilation in regulating mode, set temperature selector knob to White range (vertical). Set 
mode control knob to 4-o'clock position. Ensure A/C button indicator is illuminated. Air will vent from upper 
and lower outlets and A/C compressor will engage. Ambient air will flow from center outlet and coolant 
circulation pump will operate. If operation is not as specified, perform the following in order:  

Check A/C button activation. See A/C BUTTON under ELECTRICAL TESTS.  

Check A/C pressure switch. See A/C REFRIGERANT PRESSURE SWITCH under ELECTRICAL 
TESTS.  

Economy Setting Not In Heating Mode 

To check economy setting without heating mode activated, set temperature selector knob to Blue range. Set 
mode control knob to the 9-o'clock position. Ensure A/C button indicator is not illuminated. Ambient air will 
flow from center outlet and A/C compressor will NOT be engaged. If operation is not as specified, perform the 
following:  

Check A/C button activation. See A/C BUTTON under ELECTRICAL TESTS.  

Economy Setting In Heating Mode 

To check economy setting with heating mode activated, set temperature selector knob to Red range. Set mode 
control knob to the 4-o'clock position. Ensure A/C button indicator is not illuminated. Heated air will flow from 
lower, upper and center outlets and A/C compressor will NOT be engaged. If operation is not as specified, 
perform the following:  

Check A/C button activation. See A/C BUTTON under ELECTRICAL TESTS.  

Recirculation Mode 

To check recirculation mode, press fresh/recirculation button. Ensure fresh/recirculation indicator is 
illuminated. Set blower speed knob to position No. 4. Blower fan noise will increase noticeably. If operation is 
not as specified, check wiring between recirculated air flap element, heater-A/C switch and No. 16 fuse (15-
amp). 

ELECTRICAL TESTS 

Voltage Supply Circuit Z50/2 

1. Connect socket box to A/C push button control unit and wiring harness. See CONNECTING TEST 

EQUIPMENT . Turn ignition on, with engine off. Connect voltmeter positive lead to socket box terminal 
No. 7 and negative lead to terminal No. 9.  

2. Voltage should be 11-14 volts. If voltage is not as specified, check voltage supply circuit Z50/2 between 

No. 16 fuse (15-amp) and connected components. See WIRING DIAGRAMS . Repair as necessary. 

 

2001 Mercedes-Benz ML320 

2000-01 MANUAL A/C-HEATER SYSTEMS ML 320, ML 430 & ML 55

  

me 

 

Ground Circuit Z50/4 

1. Connect socket box to A/C push button control unit wiring harness connector. See CONNECTING 

TEST EQUIPMENT . Turn ignition off. Ensure A/C push button control unit is not connected to socket 
box.  

2. Connect ohmmeter positive lead to socket box terminal No. 9 and negative lead to body ground. 

Resistance should be zero. If resistance is not as specified, check control unit ground circuit Z50/4. See 
WIRING DIAGRAMS . Repair as necessary.  

In-Vehicle Temperature Sensor 

1. Connect socket box to A/C push button control unit and wiring harness. See CONNECTING TEST 

EQUIPMENT . Connect voltmeter positive lead to socket box terminal No. 12 and negative lead to 
terminal No. 9.  

2. Turn ignition on. Turn temperature control knob to Red range detent. Voltage should be 1.9 volts at 68°F 

(20°C). If voltage is as specified, go to next step. If voltage is not as specified, check in-vehicle 
temperature sensor circuits. See WIRING DIAGRAMS . Repair as necessary. If circuits are okay, 
replace in-vehicle temperature sensor.  

3. Turn ignition off. Disconnect test cable from A/C push button control unit. Connect ohmmeter positive 

lead to socket box terminal No. 2 and negative lead to terminal No. 12. Measure temperature sensor 
resistance at specified temperatures. See IN-VEHICLE TEMPERATURE SENSOR RESISTANCE 
table.  

4. If resistance is not as specified, check wiring harness and connectors between A/C push button control 

unit, in-vehicle temperature sensor, blend air flap actuator position sensor and temperature regulator 
switch. Repair as necessary.  

IN-VEHICLE TEMPERATURE SENSOR RESISTANCE 

Icing Protection Temperature Sensor 

1. Connect socket box to A/C push button control unit and wiring harness. See CONNECTING TEST 

EQUIPMENT . Connect voltmeter positive lead to socket box terminal No. 11 and negative lead to 
terminal No. 9.  

2. Turn ignition on. Voltage should be 2.0-2.4 volts at 32°F (0°C) and 1.4-1.8 volts at 59°F (15°C). If 

voltage is as specified, go to next step. If voltage is not as specified, check icing protection temperature 
sensor circuits. See WIRING DIAGRAMS . Repair as necessary. If circuits are okay, replace icing 
protection temperature sensor.  

3. Turn ignition off. Disconnect test cable from A/C push button control unit. Connect ohmmeter positive 

lead to socket box terminal No. 3 and negative lead to terminal No. 11. Measure temperature sensor 
resistance at specified temperatures. See ICING PROTECTION TEMPERATURE SENSOR 
RESISTANCE
 table.  

Sensor Temperature - °F (°C)

Ohms

68 (20)

2100

77 (25)

1700

104 (40)

900

 

2001 Mercedes-Benz ML320 

2000-01 MANUAL A/C-HEATER SYSTEMS ML 320, ML 430 & ML 55

  

me 

 

 

 

 

 

 

 

 

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