Climate control system 83

General information

The automatic climate control system is essentially the same as the system installed in model 129.
Differences as compared to model 129 are described.
For environmental reasons, ozone-friendly refrigerant R 134a replaces the familiar refrigerant R 12 used
previously. The filling capacity is 2.6 lbs. (1.2 kg), or 3.0 lbs. (1.4 kg) if equipped with the rear
passenger compartment climate control system. For additional information on R 134a, refer to
Introduction Manual "New Refrigerant R 134a for Automatic Climate Control".
The rear passenger compartment climate control system is standard equipment in model 140.057, and
is a special order option in all other model 140 vehicles.
The activated charcoal filter is standard equipment in models 140.051/057, and is optional in all other
model 140 vehicles.
Ventilation

P83-0460-55
A Fresh air C Warm air
B Recirculated air D Exhaust air
Climate control system 83

The air flow direction from the under-dash air

outlets can be changed by disengaging the outlet
and repositioning it as desired. The illustration
depicts the basic adjustment for the driver-side
footwell.

Location of air outlets in

under-dash panel
P83-3321-13

Location of rear air outlet

(in models without rear
passenger compartment
climate control system)
P83-3245-13

Location of ventilation check

flaps (4) for exhaust air (rear
bumper tip area)

P83-3246-13
Climate control system 83

P83-0442-55
Air flow, heating and ventilation

A Fresh air
B Recirculating air
C Warm air

Dust filter and ventilation

Dust filter
The fresh air dust filter (1) is installed ahead of
the blower motor and separates dust particles
from air entering the passenger compartment.
Depending on their size, the dust particles are
filtered up to 100% (e.g. pollen).
In models equipped with the activated charcoal
filter, the underside of the dust filter features an
activated charcoal layer.
In the air recirculation mode, air is directed
through a separate interior filter. This
recirculated air filter is of a different composition
than either of the fresh air dust filters described
above. P83-3238-13
Climate control system 83

Dust filter on vehicles with

activated charcoal filter

P83-3259-13

Dust filter on vehicles without

activated charcoal filter

P83-3318-13

The recirculated air filter (2) is located in the front

passenger footwell.

P83-3262-13A

Fresh air dust filter

Filter replacement is recommended every 2 years or 15,000 miles. In areas of high dust contamination
or strong odors, an earlier replacement interval is recommended.
Recirculated air filter
Recirculated air filter replacement is recommended every 2 years or 30,000 miles. An earlier
replacement interval is recommended in areas of high dust contamination.
These filters cannot be cleaned.
Climate control system 83

Activated charcoal filter

As an automotive first, an activated charcoal

filter is optionally available (standard equipment
in models 140.051/057). Together with the
filtration of dust, pollen and spores, this filter also
provides an effective reduction of odors and
contaminants from auto emissions, industrial
plants and other caustic sources.

1 Vacuum connection for

removal of activated
charcoal filter

P83-3260-13

The activated charcoal filter is switched on or off

by means of an electrical switch with indicator
lamp (S24/2). Air is directed to the filter via a
motor controlled bypass flap.
When selecting the defrost or "EC" settings, the
activated charcoal filter is switched off by the
pushbutton control unit (N22).

S24/2 Activated charcoal filter switch

N22 ACC pushbutton control unit
P83-3271-13A

When switching off the ignition, the flap position selected last is stored in memory and the previous
functions will resume upon restart. However, the activated charcoal filter is switched off (bypass flap
position open).
Upon switching on the activated charcoal filter, the blower motor control voltage is increased within 1
minute. This assures a constant air volume from the blower motor.
Activated charcoal filter replacement
Every 60,000 miles or:
• Every 30,000 miles of frequent vehicle operation in heavily contaminated environments (severe
operating conditions),
• In case customer requests replacement due to personal health interests,
• In case of excessive filter contamination with resulting loss of efficiency and/or continuous odor.
The activated charcoal filter cannot be cleaned.
The filter is held in place by means of a collapsible seal. By applying vacuum to a connection on the
filter seal (see illustration on previous page), the seal flattens, allowing easy removal and reinstallation of
the activated charcoal filter.

Special precautions must be observed to prevent damage to the activated charcoal filter when cleaning
or painting the vehicle. Mask off the air inlet with plastic prior to using any dewaxers, paints, or solvents
near the interior compartment ventilation intake duct and engine hood louvers. If this precaution is not
observed, the solvents or other fluids and their vapors may destroy the activated charcoal filter.
Climate control system 83

Automatic climate control

Component locations in passenger compartment

P83-5006-57
B10/2 Left heater core temperature sensor B10/6x1 Connector, evaporator temperature sensor
B10/3 Right heater core temperature sensor N22 ACC pushbutton control unit
B10/4 In-car temperature sensor with aspirator blower Y11 Switchover valve unit, 15-connection (multiplex)
B10/6 Evaporator temperature sensor
Climate control system 83

Component locations in engine compartment

P83-5029-57
A9 A/C compressor A9x1 Connector, A/C compressor
A31m1 Coolant circulation pump B12 Refrigerant pressure sensor
A32m1 Blower motor M4m1 Left auxiliary fan
A32m2 Activated charcoal filter actuator M4m2 Right auxiliary fan
A32n1 Blower motor regulator 43 Vacuum element for main air flap, left
A31y1 Left duovalve 44 Vacuum element for main air flap, right
A31y2 Right duovalve 82 Expansion valve

ACC pushbutton control unit (N22)

Temperature regulation and air distribution can
be controlled separately for the left or right sides.
The selected temperature is indicated on
individual left and right displays and may be
displayed in either °F or °C. Air volume, air
distribution and temperature selection is
controlled by the pushbutton control unit (N22).
The blower motor can be controlled manually by
a selector wheel with detent positions at "MIN",
center position "AUTO" and "MAX".

P83-3271-13B
Climate control system 83

Switching center air outlet from warm to cool air

With the center air outlet open and the system in the heating mode, the outlet can be switched to
warmer air by pressing the red button (W) or switched to cooler air by pressing the blue button (K).
This switchover between warmer or cooler air is controlled by the blend air flaps (45 and 46) and diverter
flaps (41 and 42). See "Automatic climate control vacuum schematic" in this section of this Introduction
Manual.
Control of center and side air outlets
The instrument panel center and side air outlets
can be controlled by means of knurled wheels
(located below the center air outlets) which
adjust the position of the air outlet flaps via
bowden cables.

P83-5143-13

M anual blower program

In addition to the automatic mode, the blower
speed can be controlled manually via the
selector wheel.
The blower speed is infinitely adjustable,
however, there are three basic settings:
MIN: Lowest blower speed
AUTO:Recommended position, to guarantee
proper operation in automatic mode
MAX: Highest blower speed
N22 ACC pushbutton control unit
P83-3271-13

Selection (Normal setting)

• The blower operates at low speed at low outside temperature and low coolant temperature.
The blower speed increases under increasing coolant temperature. With the engine at operating
temperature, the blower operates at various stepless blower speeds.
• In the heating mode, blend air flows from the footwell and side air outlets, as well as bleed air from
the defroster ducts.
• In the cooling mode, cool air flows from the center and side air outlets. During mode changes,
cool air also flows from the defroster ducts.
• Mode changes take place automatically in steps via two-stage elements for the defroster ducts and
footwell air outlets. As a result, the footwell, center and defroster air outlets/ducts can be open at the
same time.
• The system automatically selects warm or cool air for the center air outlets as long as the warm (red)
or cool (blue) manual override button is not selected. As soon as one of the pushbuttons is pressed,
the automatic function of the center air outlet is canceled.
• A/C compressor engagement occurs at outside temperatures above approx. 3 °C. This maintains
evaporator temperature at approx. 3 to 5 °C (37to 41 °F).
Climate control system 83

Selection (Defrost)
• The blower operates immediately at almost maximum blower speed regardless of coolant
temperature. With the blower selector wheel set to "MAX", the blower operates immediately at
maximum blower speed.
• Both duovalves open, providing full and unregulated heat output.
• Coolant circulation pump runs continuously.
• Defroster ducts are open and all other air outlets are closed. The side air outlets can be opened or
closed manually.
• The system operates with 100% fresh air. Air recirculation and activated charcoal filter
(if equipped) selections are canceled.
• A/C compressor engagement occurs above 3 °C (37 °F).

Selection (Economy)

This selection corresponds to the function, however, the A/C compressor is continuously switched
off.

M anual flap regulation

Air flow to windshield

Air flow to windshield, footwell area and doors

Air flow to footwell area and doors

Selection "0"(Off)
• Blower motor off,
• Duovalves closed,
• Main air flap closed,
• A/C compressor switched off,
• Coolant circulation pump not running,
• Engine coolant temperature regulation in operation (auxiliary fan control).
Climate control system 83

Selection (Residual engine heat utilization)

If the engine is switched off after having reached operating temperature, the passenger compartment
can be heated for a period by pressing the button. This feature is only available with the ignition
key in positions 0 or 1, or with the ignition key removed.
After pressing the switch, the system operates automatically as follows:
• Passenger compartment temperature is maintained according to temperature set on selector wheels,
• Blower motor operates at low speed,
• Footwell flaps open,
• Defroster flaps in bleed air position,
• Diverter flaps closed,
• Blend air flaps closed,
• Main air flap at 80% recirculated air,
• Coolant temperature >50 °C,
• Battery voltage 11-14 volts,
• Automatically cancels after 30 minutes,
• Automatically cancels when ignition is switched on.

Selection (Air recirculation)

After pressing the air recirculation switch, the air recirculation flap is positioned to 100% recirculated air
with the A/C is switched on and the outside temperature above 7°C (42 °F).
After 20 minutes, the system automatically switches to fresh air or to automatically controlled
recirculated air.
The system switches to fresh air (or to automatically controlled recirculated air) after 5 minutes if the A/C
compressor is switched off (as in selection ) or if the outside temperature is below 7°C (42 °F).

Automatic engagement of air recirculation

Automatic engagement of air recirculation is dependent on the temperature difference between the
selected temperature, ambient temperature and in-car temperature.
Diagnostics with malfunction memory
The ACC pushbutton control unit (N22) is
equipped with diagnostics with malfunction
memory. Brief malfunctions are registered,
stored in memory and can be read via the
temperature displays (arrows), or impulse
counter connected to the test connection for
diagnosis (X11/4). Using the two temperature
displays (arrows), special diagnostic programs
can be used which display actual measured
sensor values, and the control signals to the air
distribution flaps.
For testing, refer to Diagnostic Manual, Climate
Control, Volume I, section 3.2.
P83-3271-13B
Climate control system 83

In-car temperature sensor with aspirator

blower (B10/4)
The in-car temperature sensor (B10/4) features
an integrated aspirator motor and is part of the
front dome lamp assembly (E15) .

P83-3298-13

Heater supplyunit (A31)

The heater supply unit (A31) is comprised of the
coolant circulation pump (A31m1) and the left
and right duovalves (A31y1, A31y2). The
impeller of the coolant circulation pump is driven
without any mechanical connection to the electric
pump motor.

P83-3249-13

Engine OFF cooling

At engine coolant temperatures greater than
100 °C, the coolant temperature is monitored for 90 seconds after switching off the ignition.
If the coolant temperature exceeds 110 °C after 90 seconds, the coolant circulation pump (A31m1) is
switched on for a maximum of
10 minutes to assist in cooling the engine. Should the coolant temperature drop below
110 °C during the 10 minute period, engine OFF cooling switches off.
During engine OFF cooling:
• Coolant circulation pump (A31m1) is ON,
• Coolant pump control relay (K30) is energized,
• Blower motor (A32m1) is OFF,
• Left and right duovalves (A31y1, A31y2) are closed, thereby opening the bypass for engine OFF
cooling.
Climate control system 83

Switchover valve unit (Y11, 15-connection)

The control of the individual air flaps occurs via
the switchover valve unit (Y11, 15-connection)
and via the single and two-stage vacuum
elements . The switchover valve unit is actuated
via multiplex control (serial data transfer) from
pushbutton control unit (N22).

P83-3250-13

The vacuum supply is provided by vacuum

distribution block (36) located in the front
passenger footwell.

P83-3250-13

Connector assignment

1 Rear passenger compartment climate control

2 Backrest lock, model 140 coupé(SEC)
3 Not used
4 Not used
5 ACC system switchover valve unit (Y11)
6 Manifold vacuum assist
(pneumatic control unit A37/A37/1)
7 Manifold vacuum
8 Not used
9 Not used
10 Not used
11 Not used
12 Not used
13 ACC vacuum storage reservoir
P83-3240-13
Climate control system 83

A/C compressor and compressor shut-off

A larger capacity swash plate type compressor
10 PA 20 is installed in all model 140 vehicles.

P83-3278-13

The base module (N16/1) disengages the A/C

compressor clutch in cases of an compressor
overload condition and resultant poly-v-belt
slippage. The base module (N16/1) will record
the disengagement as a malfunction and store
this information in memory.
For testing and diagnosis, refer to Diagnostic
Manual, Chassis and Drivetrain, section 1.0.

X11/4 Test connection for diagnosis

P83-3252-13

Expansion valve (82)

Location of expansion valve in component

compartment below water tray

P83-3258-13
Climate control system 83

Auxiliaryfans and auxiliaryfan control

All model 140 vehicles are equipped with two
auxiliary fans. The current draw under operation
in the 3rd stage is 35 amperes at 13 volts battery
voltage. The auxiliary fans are protected by
a 30 ampere fuse in the maxi-fuse box F2.

P83-3253-13A

A refrigerant pressure sensor (B12) on the

receiver-drier is installed in place of the two
previous pressure switches.
The ACC pushbutton control unit (N22) receives
an input from the sensor (B12)to provide low
pressure/high pressure A/C compressor cut-out,
and to control the 3 stages of the auxiliary fans
(see "Auxiliary fan switchpoints").
The auxiliary fans are controlled by the ACC
pushbutton control unit (N22) via auxiliary fan
relays (K9, K9/1) and pre-resistors (R15, R15/1).

P83-3248-13

Location of pre-resistor R15 and R15/1

between auxiliary fans

P83-3309-13
Climate control system 83

Location of relays K9, K9/1, K30

P83-3253-13

Auxiliaryfan switchpoints 1st stage 2nd stage 3rd stage

Refrigerant pressure in bar 14 on 17on 20 on
12 off 14 off 17off
Coolant temperature sensor (B10/8) in °C 100 on 107on 115 on
95 off 100 off 107off
Voltage supplied to auxiliary fans 7 9 12

In the 1st stage, the auxiliary fans:

• Do not engage at ambient temperatures < +5 °C,
• Engage at ambient temperatures > +10 °C.

Location of coolant temperature sensor

B10/8, engine 104

P83-3255-13

Location of coolant temperature sensor

B10/8, engine 119

P83-3257-13
Climate control system 83

Location of coolant temperature sensor

B10/8, engine 120

P83-3256-13

Location of coolant temperature sensor

B10/8, engine 603

P83-5154-13

Blower motor (A32m1)

The blower motor is located behind the dust
filters.
The blower regulator (A32n1) is similar to the
one installed in model 129. The circuit is short
circuit protected and requires no additional fuse
protection.

P83-3299-13
Climate control system 83

Diode matrix(V2)
A control voltage from the blower regulator
greater than 2.5 volts will increase the engine
idle speed via the diode matrix (V2).

P82-3067-13

Air outlets.automatic climate control/rear passenger compartment climate control

P83-0446-57
a Recirculated air intake, automatic climate control d Center rear footwell air outlet, air from rear
b Recirculated air intake, rear passenger passenger compartment climate control
compartment climate control
c Left and right rear footwell air outlets, air from
automatic climate control
Climate control system 83

Vacuum schematic, automatic climate control

P83-5002-59
Y11 Switchover valve unit, 15-connection 39 Vacuum element, diverter flap, left side air outlet
0 Vacuum distribution block 40 Vacuum element, diverter flap, right side air outlet
1 Left diverter flap 41 Vacuum element, diverter flap, left center air outlet
2 Right diverter flap 42 Vacuum element, diverter flap, right center air outlet
3 Left blend air flap 43 Vacuum element. main air flap, rear
4 Right blend air flap 44 Vacuum element, main air flap, front
5 Side air outlet diverter flap 45 Vacuum element, blend air flap, left center air outlet
6 Left defroster flap, long stroke 46 Vacuum element, blend air flap, right center air outlet
7 Left defroster flap, short stroke 47 Vacuum element, left footwell flap
8 Right defroster flap, long stroke 48 Vacuum element, right footwell flap
9 Right defroster flap, short stroke 49 Vacuum element, air recirculation flap
10 Main air flap, short stroke
11 Main air flap, short stroke hbl light blue
12 Left footwell flap, long stroke drt dark red
13 Left footwell flap, short stroke ge yellow
14 Right footwell flap, short stroke mgn medium green
15 Right footwell flap, long stroke gr grey
rt red
1 ACC vacuum storage reservoir ws white
2 Connection for ACC vacuum storage reservoir sw black
36 Vacuum distribution block dgn dark green
37 Vacuum element, left defroster flap gn green
38 Vacuum element, right defroster flap
Climate control system 83

Coolant circuit, automatic climate control

P83-0443-57
A Coolant inlet 3 Heater core, heating system
B Coolant return flow 6 Radiant heat for windshield (wiper system)
1 Engine 7 Thermovalve, radiant heat for windshield (wiper
2 Heater supply unit system)
8 Thermovalve, windshield washer fluid heater
Climate control system 83

Coolant circuit, automatic climate control/rear passenger compartment climate control

P83-0444-57
A Coolant inlet 4 Heater supply unit, rear passenger compartment
B Coolant return flow climate control
1 Engine 5 Heater core, rear passenger compartment
2 Heater supply unit climate control
3 Heat exchanger, heating system 6 Radiant heat for windshield (wiper system)
7 Thermovalve, radiant heat for windshield
(wiper system)
8 Thermovalve, windshield washer fluid heater
Climate control system 83

Rear passenger compartment climate control

Component locations in passenger compartment

P83-3314-35
B10/9 Left heater core temperature sensor N29/2 Electronic blower regulator (rear passenger
B10/10 Right heater core temperature sensor compartment climate control)
B10/11 Rear evaporator temperature sensor 107 Refrigerant injection valve
M2/1 Rear blower motor c Coolant inlet
d Coolant return flow
Climate control system 83

Component locations not in passenger compartment

P83-5018-57
A31/1m1 Coolant circulation pump (right front wheelhousing) F4 Rear fuse box (17-fuse, in trunk)
A31/1y1 Left duovalve Y67 Rear refrigerant shut-off valve (left front wheelhousing)
A31/1y2 Right duovalve

A rear passenger compartment climate control system is standard equipment in model 140.057, and is
available as a special order option in all other model 140 vehicles.
The rear passenger compartment climate control system is a separate heating and cooling system
which utilizes components familiar from the automatic climate control.
The refrigerant circuit for rear passenger compartment cooling is connected in parallel with the existing
air conditioning system.
The refrigerant supply to the rear evaporator is controlled by a solenoid valve, located in the left front
wheelhousing.
For rear passenger compartment cooling, the (front) automatic climate control must be switched on.
For rear passenger compartment heating, it is not necessary to switch on the (front) automatic climate
control. The systems operate independent from one another.
The left and right air outlet temperature can be separately adjusted via the left and right temperature
wheels (1, 2).
Climate control system 83

The rear passenger compartment climate control

is switched on/off via the blower speed selector
wheel (3). The system is switched on with the
blower speed selector wheel (3) in any position
except the "0" detent.

P83-0435-13

The blower speed control is stepless and can be selected between 0 (detent, system OFF) and
maximum speed.
The electronic blower regulator (N29/2) is similar in function to the one installed in model 129.
The rear passenger compartment climate control operates exclusively with recirculated air.
With the rear air conditioner switched on, the
flaps for the rear footwell areas are closed by the
(front) automatic climate control system. This
changeover takes place via the rear tunnel flap
vacuum valve (Y67/1) and vacuum elements (50
and 51).

P83-3305-13

The slide regulator (6) controls the air distribution

of the rear passenger compartment climate
control between the rear center air outlets and
rear footwell areas. The direction of air flow of
the rear center air outlets is adjustable with the
louvers (4) and (5).

P83-0435-13

With all temperature selection wheels ( front and rear) set to maximum red detent for maximum heat, the
flaps for the rear footwell areas remain open.
Climate control system 83

Using the two temperature selector wheels (1,

2), the heating or cooling capacity of the rear
passenger compartment climate control can be
controlled separately left and right, in
accordance with the in-car temperature sensor
(B10/4).

P83-0435-13

With the air conditioning system switched on, the system operates basically in a re-heat mode. This
means that the intake air is first cooled by the evaporator and then heated by the heater core as needed.
The rear heater supply unit (A31/1) is located
behind the side protection panel of the right front
fender. The function and design (coolant
circulation pump/left and right duovalves)
corresponds to the supply unit of the front
heating system.

Location of rear heater supply unit

(A31/1), behind right front fender
side protection panel
P83-3243-13

Instead of the familiar expansion valve,

refrigerant is injected into the rear evaporator by
means of a refrigerant injection valve (107).
The refrigerant supply is controlled by a rear
refrigerant shut-off valve (Y67).

Location of rear refrigerant shut-off

valve (Y67), behind left front fender
side protection panel

P83-3306-13
Climate control system 83

Arrow indicates the direction of refrigerant flow

P83-3311-13

The rear passenger compartment climate control

is protected by the fuse box F4.

P80-2232-13
Climate control system 83

Vacuum schematic, rear passenger compartment climate control

P83-5004-59
Y67/1 Rear tunnel flap vacuum valve 50 Vacuum element, right rear footwell
1 Vacuum reservoir 51 Vacuum element, left rear footwell
36 Vacuum distribution block