Mercedes-Benz ML320. Manual — part 648

4. If resistance is not as specified, check wiring harness between temperature sensor and control unit. Repair

as necessary. If wiring harness is okay, replace icing protection temperature sensor.

ICING PROTECTION TEMPERATURE SENSOR RESISTANCE

Activation Voltage Temperature

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. 2 and negative lead to
terminal No. 9.

2. Turn ignition on. Turn temperature control knob to Blue range detent. Voltage should be more than 2.0

volts. Turn temperature control knob from Blue range detent to Red range detent. Voltage should be more
than 3.0 volts.

3. If voltage is as specified, go to next step. If voltage is not as specified, check recirculated air switch

circuits. See WIRING DIAGRAMS . Repair as necessary. If circuits are okay, replace recirculated air
switch.

4. Connect voltmeter positive lead to socket box terminal No. 5 and negative lead to terminal No. 9. Turn

ignition on. Turn temperature control knob to Blue range detent. Voltage should be more than 3.0 volts.
Turn temperature control knob from Blue range detent to Red range detent. Voltage should be more than
4.0 volts.

5. If voltage is not as specified, check recirculated air switch circuits. See WIRING DIAGRAMS . Repair

as necessary. If circuits are okay, replace recirculated air switch.

Blend Air Flap Actuator Motor

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. 1 and negative lead to
terminal No. 9.

2. Turn ignition on. Turn temperature control knob to Blue range detent. Voltage should be less than one

volt. Turn temperature control knob from Blue range detent to Red range detent. Voltage should be 11.0-
14.0 volts.

3. If voltage is as specified, go to next step. If voltage is not as specified, check blend air flap actuator motor

wiring harness circuits. See WIRING DIAGRAMS . Repair as necessary. If circuits are okay, replace
blend air flap actuator motor.

4. Connect voltmeter positive lead to socket box terminal No. 8 and negative lead to terminal No. 9. Turn

ignition on. Turn temperature control knob to Red range detent. Voltage should be less than one volt.
Turn temperature control knob from Red range detent to Blue range detent. Voltage should be 11.0-14.0
volts.

5. If voltage is as specified, go to next step. If voltage is not as specified, check blend air flap actuator motor

wiring harness circuits. See WIRING DIAGRAMS . Repair as necessary. If circuits are okay, replace

Sensor Temperature - °F (°C)

Ohms

43 (6)

3600

59 (15)

2300

72 (22)

1700

77 (25)

1500

2001 Mercedes-Benz ML320

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

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blend air flap actuator motor.

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

lead to socket box terminal No. 1 and negative lead to terminal No. 8. Resistance should be 120 ohms.

7. If resistance is not as specified, check blend air flap actuator motor circuits. See WIRING DIAGRAMS .

Repair as necessary. If circuits are okay, replace blend air flap actuator motor.

A/C Button

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. 10 and negative lead to
terminal No. 9.

2. Turn ignition on. Depress A/C button switch to on position and set blower speed knob to position No. 4.

Ensure A/C button indicator is illuminated. Voltage should be less than one volt. Depress A/C button
switch to off position with A/C button indicator not illuminated or set blower speed knob to off position.
Voltage should be 11-14 volts.

3. If voltage is as specified, go to next step. If voltage is not as specified, check A/C button wiring harness

circuits. See WIRING DIAGRAMS . Repair as necessary. If circuits are okay, replace A/C button
switch.

4. Turn ignition on. Depress A/C button switch to on position and set blower speed knob to position No. 4.

Ensure A/C button indicator is illuminated. Connect voltmeter positive lead to socket box terminal No. 4
and negative lead to terminal No. 9. Voltage should be more than 3.0 volts.

5. Connect Fused Jumper Wire (124 589 37 63 00) between socket box terminals No. 4 and 11. Depress A/C

button switch to on position and set blower speed knob to position No. 4. Ensure A/C button indicator is
illuminated. Measure voltage. Voltage should be less than one volt.

6. If voltage is not as specified, check A/C button wiring harness circuits. See WIRING DIAGRAMS .

Repair as necessary. If circuits are okay, replace A/C button switch.

A/C Refrigerant Pressure Switch

1. Turn ignition off. Disconnect refrigerant pressure sensor connector. Turn ignition on. Connect voltmeter

positive lead to pressure sensor harness connector terminal "B" (Pink wire) and negative lead to terminal
"A" (Tan wire). Voltage should be 4.75-5.25 volts.

2. If voltage is as specified, replace A/C refrigerant pressure sensor. If voltage is not as specified, check

wiring harness between refrigerant pressure sensor and All Activity Module (AAM). See WIRING
DIAGRAMS . Repair as necessary. If circuits are okay, replace AAM and retest A/C system.

Outside Temperature Sensor

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

EQUIPMENT . Turn ignition off. Connect ohmmeter positive lead to socket box terminal No. 12 and
negative lead to terminal No. 3.

2. Disconnect test cable from A/C push button control unit. See OUTSIDE TEMPERATURE SENSOR

RESISTANCE table. If resistance is not as specified, check wiring harness between outside temperature
sensor and A/C push button control unit. See WIRING DIAGRAMS . Repair as necessary. If wiring
harness is okay, replace outside temperature sensor.

2001 Mercedes-Benz ML320

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

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OUTSIDE TEMPERATURE SENSOR RESISTANCE

READING ACTUAL VALUES WITH HHT

Connect Hand-Held Tester (HHT) to DLC and follow displayed procedures. Actual values displayed on HHT
show normal operation value of A/C systems or components. See ACTUAL VALUES table. If value is not as
specified, check system or components in order. Repair as necessary.

ACTUAL VALUES

REMOVAL & INSTALLATION

Sensor Temperature - °F (°C)

Ohms

68 (20)

2100

77 (25)

1700

104 (40)

900

122 (50)

600

Step

(1)

Test Condition

Value

System/Component

01

. .

11-14 Volts

Voltage Supply Wiring (Circuit

No. 30) & Battery

02

Engine Operating At

Normal Temperature

About 176°F (80°C)

Wiring, ECT Sensor & AAM

03

Ignition ON

Ambient Air Temperature

About 68°F (20°C)

Wiring, Outside Temperature

Sensor & AAM

04

Ignition ON, Blower At

Stage 4

ON/OFF

Wiring, Blower Motor Relay,

Blower Motor & AAM

05

Ignition ON

ON/OFF

Wiring, Engine Cooling Fan

Stage 1, Aux. Fan & AAM

08

Ignition ON

ON/OFF

Wiring, Coolant Circulation Pump

Relay, Coolant Circulation Pump

& AAM

09

Engine On, A/C Indicator

On, Blower Motor At

Stage 4

Refrigerant Pressure At

174 psi (12 bar)

(2)

Refrigerant Pressure Sensor

10

Engine On, A/C Indicator

On, Blower Motor At

Stage 4

ON/OFF

(3)

AAM, A/C Compressor

11

Ignition ON, Activate

A/C System

YES/NO

Wiring, A/C Push Button Control

Module, AAM

(1)

Step numbers not shown are not used.

(2)

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

(3)

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

2001 Mercedes-Benz ML320

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

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A/C EVAPORATOR HOUSING UNIT

Removal & Installation

1. Drain engine coolant. Remove coolant expansion reservoir nuts, disconnect hoses and remove reservoir.

Discharge A/C system, using approved refrigerant recovery/recycling equipment.

2. Remove expansion valve self-locking nut and discard. See Fig. 5 . Disconnect refrigerant lines from

expansion valve. Plug exposed refrigerant lines to protect A/C system from moisture and debris.

3. Remove instrument panel. See INSTRUMENT PANEL . Remove Electronic Transmission Control

(ETC) module. See Fig. 4 . Disconnect air mix flap actuator connector.

4. Disconnect recirculated air flap element. Disconnect evaporator temperature sensor. Disconnect blower

motor resistor and blower motor connectors. Remove A/C push button control module. Release wiring
harness.

5. Remove insulating mat. See Fig. 5 . Disconnect water drain hose from bottom of A/C housing. Release

A/C housing-to-air distributor clips and remove A/C housing upward. To install, reverse removal
procedure. Recode radio. See RECODING RADIO under PROGRAMMING.

WARNING:

To avoid injury from accidental air bag deployment, read and carefully
follow all SERVICE PRECAUTIONS and DISABLING & ACTIVATING AIR
BAG SYSTEM procedures in AIR BAG SYSTEM SAFETY article in
GENERAL SERVICING.

CAUTION: Before disconnecting battery, obtain 5-digit radio security code from

vehicle owner. Radio will be disabled until properly recoded.

2001 Mercedes-Benz ML320

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

me