engine MERCEDES-BENZ ML320 1997 Complete Repair Manual

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.

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

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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 ConditionValueSystem/Component
01.....11-14 VoltsVoltage Supply Wiring (Circuit
No. 30) & Battery
02Engine Operating At
Normal TemperatureAbout 176°F (80°C)Wiring, ECT Sensor & AAM
03Ignition ONAmbient Air Temperature
About 68°F (20°C)Wiring, Outside Temperature
Sensor & AAM
04Ignition ON, Blower At
Stage 4ON/OFFWiring, Blower Motor Relay,
Blower Motor & AAM
05Ignition ONON/OFFWiring, Engine Cooling Fan
Stage 1, Aux. Fan & AAM
08Ignition ONON/OFFWiring, Coolant Circulation Pump
Relay, Coolant Circulation Pump
& AAM
09Engine On, A/C Indicator
On, Blower Motor At
Stage 4Refrigerant Pressure At
174 psi (12 bar)(2) Refrigerant Pressure Sensor
10Engine On, A/C Indicator
On, Blower Motor At
Stage 4ON/OFF(3) AAM, A/C Compressor
11Ignition ON, Activate
A/C SystemYES/NOWiring, 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.

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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.

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2000-01 MANUAL A/C-HEATER SYSTEMS ML 320, ML 430 & ML 55
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6. Remove A-pillar panel trim. Remove instrument cluster. Remove defroster vent cover. Remove air vents
and side air nozzles. With assistance, remove upper instrument panel.
7. Remove passenger-side air bag. Remove right side lower instrument panel cover. Remove instrument
panel carrier screws from A/C housing unit. Remove left side lower instrument panel cover.
8. Remove insulating mat between steering column and instrument panel carrier. Remove steering column
bolts and nuts from instrument panel carrier. See Fig. 8
. Remove instrument panel carrier center tunnel
bolts. Disconnect steering column connectors.
9. Remove wiring harness from instrument panel carrier. Remove wiper washer system. Remove instrument
panel carrier nuts from engine compartment side of firewall.
10. Remove A-pillar bolt covers and remove instrument panel carrier A-pillar bolts. With assistance, remove
instrument panel carrier through passenger door. To install, reverse removal procedure.
11. Ensure instrument panel bottom section guide tongues "B" are seated into instrument panel upper section
mounts. See Fig. 8
. Tighten nuts and bolts to specification. See TORQUE SPECIFICATIONS .
Recode radio. See RECODING RADIO
under PROGRAMMING.
Fig. 7: Removing Instrument Panel Bottom Section

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

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2000-01 MANUAL A/C-HEATER SYSTEMS ML 320, ML 430 & ML 55
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BLOWER MOTOR FUNCTION - GF83.10-P-2170-01GI
Function
The AAC push-button control module (N22) passes a control voltage of 0-6 V to the blower regulator (A32n1)
via the AC bus. Depending on the control voltage which is present, this then regulates the blower motor
(A32m1) operating voltage of 0-12 V. This facilitates blower speed control of 0-100 %.
The blower motor actuation (operating voltage) is influenced by the following factors:
Blower power setting manual or AUTO
Operating functions:
Air distribution
AC OFF mode
Residual engine heat mode (actuation limited to 5 V)
Mode status (heating, cooling)
Coolant temperature
Vehicle speed
Fresh air/recirculation flap setting
Flap positions
Terminal 15 (blower ON), starter running (blower OFF)
BLOWER MOTOR LOCATION/TASK/DESIGN/FUNCTION - GF83.10-P-2170GI
MODEL 163 as of 1.9.01 with CODE (580a) Automatic air conditioning
Blower, task
The rear blower motor (M2/1) serves to improve ventilation and cooling
in the rear.
The air that is drawn in by the blower in the evaporator housing is led to
the rear blower motor (M2/1) via air ducts.
The rear blower motor (M2/1) increases the flow of air.

Blower,
function GF83.10-P-
2168-01GI

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1998-2005 HVAC Climate Control - 163 Chassis
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Fig. 27: Identifying Blower Motor
REAR SHUTOFF FLAP ACTUATOR MOTOR FUNCTION - GF83.10-P-2171-01GI
Function
Pressing the rear compartment air distribution button ( ) on the AAC push-button control module (N22)
actuates the rear shutoff flap actuator motor (M12/2) via the AC bus. The rear shutoff flap actuator motor
(M12/2) therefore controls the rear shutoff flap, which opens and controls the air supply to the rear blowout
ducts.

Blower
motor
locationThe blower motor (A32m1) is to the bottom right of the evaporator housing
below the glove compartment.
Blower
motor task
In fresh air mode the blower motor draws in fresh air via the fresh
air/recirculating air flap. In recirculating air mode, air from the vehicle interior
is drawn into the evaporator housing via the fresh air/recirculating air flap.
When residual engine heat utilization is being used, the blower motor circulates
the air around the interior.


Blower
motor
design
The blower motor is designed as a radial blower.

Blower
motor
function
GF83.10-P-
2170-01GI

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1998-2005 HVAC Climate Control - 163 Chassis
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HEATER CIRCUIT FUNCTION - GF83.20-P-2003GH
MODEL 163
Fig. 33: Identifying Heater Circuit Function

Function
The coolant pump (5) pumps cold coolant through the engine. The coolant absorbs the engine's heat and
becomes heated. The heated coolant is then conducted through the heat exchanger (2). The air blowing by the
heat exchanger (2) is heated and conducted into the vehicle interior.
The coolant is routed over the coolant return (A) and the heating water circulation pump (6) back to the coolant
pump (5).
By far the greater percentage of the coolant does not flow through the heat exchanger (2), but from the engine to
the coolant thermostat (4). Depending on the water temperature, this conducts the water through the radiator (3)
or directly to the coolant pump (5).
HEATER CONTROLS, FUNCTION - GF83.20-P-2004GH
Heater housing position/task/function GF83.20-P-2110GC
Heating system heat exchanger, location/ purpose/function GF83.20-P-2108GC
Heater water circulation pump, location/task/ functionas of 1.09.01GF83.20-P-2109GI

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1998-2005 HVAC Climate Control - 163 Chassis
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Fig. 35: Identifying Heater Core
HEATING WATER CIRCULATION PUMP FUNCTION - GF83.20-P-2102-01GI
Function
The quantity of coolant delivered to the heat exchanger when the engine is running is dependent on the coolant
pump. The heating water circulation pump ensures that a constant and bubble-free flow of water is present at
the heat exchanger during residual engine heat utilization, even at low engine speeds.
Initialization of the heating water circulation pump is carried out via the AAC push-button control module
(N22).
Switch-on conditions
Ignition ON
Stationary heater/ON
Enable conditions at residual engine heat complied with
Special conditions
At ambient temperatures of less than -20°C several starting attempts are made, in order to ensure that the
heating water circulation pump goes into operation.
To this end the heating water circulation pump is switched off in intervals of 1 minute for 5 seconds, until the
coolant or blow-out temperature is +20°C higher than the ambient temperature.
Switch-off conditions
Ignition OFF and overshoot time expired
Stationary heater OFF
Residual engine heat OFF and overshoot time expired
Enable conditions at residual engine heat no longer complied with
Enable conditions at residual engine heat

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1998-2005 HVAC Climate Control - 163 Chassis
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The heating water circulation pump runs in any event 1 minute after starting residual engine heat operation. The
overshoot conditions at least will be fulfilled.
Overshoot conditions
Coolant temperature 100°C --> overshoot time 5 minutes
Coolant temperature >100°C --> overshoot time 10 minutes
HEATER HOUSING POSITION - GF83.20-P-2103-01GH
The heater housing (1) is located beneath the instrument panel.
Fig. 36: Identifying Heater Housing

HEATER BOX FUNCTION - GF83.20-P-2103-02GH
Operating condition: Heating

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1998-2005 HVAC Climate Control - 163 Chassis
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