1996 Audi A6 Quattro

HEAT, VENTILATION & A/C 1995-96 Auto. A/C-Heater Systems

HEAT, VENTILATION & A/C

1995-96 Auto. A/C-Heater Systems

A/C SYSTEM SPECIFICATIONS

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 RESTRAINT SYSTEM article in
ACCESSORIES/SAFETY EQUIPMENT SECTION.

AUTOMATIC A/C-HEATER SYSTEMS SPECIFICATIONS

Application Specifications
Compressor Type Zexel 6-Cyl. Or Nippondenso
Compressor Belt Tension (1)
System Oil Capacity (2) 7.8-9.2 ozs.
Refrigerant (R-134a) Capacity
Nippondenso Compressor 26.5-28.2 ozs.
Zexel Compressor 23.0-24.8 ozs.
System Operating Pressures (3)
Low Side 26-29 psi (1.8-2.0 kg/cm2 )
High Side 79.8 psi (5.61 kg/cm2 )
(1) Belt tension is automatically adjusted by belt tensioner.
(2) Use SP-10 Oil (Part No. G 052 154 A2) on Zexel compressor. Use SP-10 Oil (Part No. G 052 300
A2) on Nippondenso compressor.
(3) Measured at 77°F (25°C). High side pressure increases from base pressure (engine off) to maximum
of 350 psi (24.6 kg/cm2 ) .

DESCRIPTION
The A/C-heater control panel has buttons to control system. Blower speed is controlled automatically according
to difference between selected temperature and interior temperature. Blower speed can also be controlled
manually.

The A/C-heater control panel left side display shows selected temperature and automatic functions. See Fig. 1 .
The right side display indicates manual functions. The A/C-heater system micro-processor, located within A/C-
heater control panel, has a self-diagnostic feature.

The A/C-heater system automatically maintains temperatures from 64°F (18°C) to 85°F (29°C). If temperature
greater than 85°F (29°C) is selected, the word HI appears in temperature display. If temperature less than 64°F
(18°C) is selected, the word LO is displayed. Selection of these temperatures overrides automatic climate
control system.
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Fig. 1: Identifying A/C-Heater Control Panel

Courtesy of AUDI OF AMERICA, INC.

OPERATION
A/C COMPRESSOR SPEED SENSOR

Zexel Compressors

Sensor is located on compressor and determines A/C compressor speed. A/C-heater control panel then
compares compressor speed to engine speed and calculates belt slippage (as a percentage). If slippage is
excessive, control panel switches compressor off.

A/C-HEATER CONTROL PANEL & AIR DISTRIBUTION

A/C-Heater Control Panel

A/C-heater control panel has a digital microprocessor that compares values from various sensors.
Microprocessor then activates appropriate flap motor and A/C compressor clutch to maintain desired
temperature. A/C clutch, blower speed, temperature/blend air door position, and mode doors are all controlled
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by A/C-heater control panel.

Air Distribution

Three buttons control air distribution. See Fig. 1 . When selected, uppermost air distribution button directs air to
windows. When middle air distribution button is selected, air is directed to dashboard outlets and rear of center
console. When lowermost air distribution button is selected, air is directed to footwells.

Automatic Mode

In this setting, air temperature, air delivery and air distribution are regulated automatically to achieve and
maintain desired interior temperature. All previously selected settings are canceled.

Blower Speed Settings

Blower speed buttons can be used to raise or lower blower speed in all operating modes. Blower speed plus (+)
button is used to raise blower speed. Minus (-) button lowers blower speed. If minus (-) button is pushed after
blower speed is set at its lowest setting, climate control system will be deactivated.

Climate control system will also be deactivated if minus (-) and plus (+) buttons are pushed simultaneously. To
reactivate system, press AUTO button, defrost button, one of temperature control buttons or blower speed plus
(+) button.

Compressor On/Off Button

This button controls A/C compressor operation.

Defrost Mode

In this setting, recirculation door is open. Blower runs at highest speed and temperature is automatically
regulated. All air is directed toward windshield.

ACTUATORS

Central Air Distribution Flap Motor

This actuator (motor) is located on front of heater box. The central air distribution flap is used to distribute
airflow to instrument panel vents or to footwell/defroster outlets. A potentiometer, inside motor, indicates
position of air distribution flap to A/C-heater control panel as a feedback value.

Footwell/Defroster Flap Motor

This actuator (motor) is located on front of heater box. The footwell/defroster flap distributes air to footwell or
defroster outlets depending on mode selected. A potentiometer, inside motor, indicates position of air
distribution flap to A/C-heater control panel as a feedback value.

Fresh Air/Recirculating Flap Motor (Vacuum Servo)

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This vacuum-operated actuator is located on left side of evaporator assembly, in air plenum. A two-way vacuum
valve is used to control the amount of vacuum applied to fresh air/recirculating flap motor. See TWO-WAY
VACUUM VALVES .

Temperature Regulator Flap Motor

This actuator (motor) is mounted on left side of heater box. See Fig. 2 . A potentiometer, inside motor, indicates
position of air distribution flap to A/C-heater control panel as a feedback value.

The temperature regulator flap is used to control air temperature in vehicle passenger compartment. Air
temperature regulation is accomplished by using two flaps, one flap before and one flap after heater core. The
temperature-regulating flap actuating mechanism also operates turbulence flap.

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Fig. 2: Identifying Automatic A/C-Heater System Components

Courtesy of AUDI OF AMERICA, INC.

AMBIENT TEMPERATURE SENSORS

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Two sensors measure outside air temperature and send input signals to A/C-heater control panel. A/C-heater
control panel measures sensor readings and lowest temperature value to calculate correction factor for interior
temperature regulation. One sensor is located in front of vehicle, behind lower air grille. Second sensor is
located in evaporator, next to fresh air flap.

FRESH AIR TEMPERATURE SENSOR

Temperature sensor is located on heater box, downstream of fresh air fan. Sensor measures temperature of air
leaving evaporator to provide quicker response time to changes of interior temperature.

FAN CONTROL UNIT

Air to passenger compartment is supplied and regulated by fan control unit. Fan control unit is mounted to
evaporator box, in air plenum, and is cooled by airflow through evaporator housing. See Fig. 3 .

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Fig. 3: Identifying Fan Control Unit & Low Pressure Switch

Courtesy of AUDI OF AMERICA, INC.

HIGH PRESSURE SWITCH

Switch controls cooling fan high speed operation. Switch is located on high pressure switch refrigerant line.
Switch is identified by its Green housing. Ensure switch closes at 206-252 psi (14.48-17.72 kg/cm2 ) . Ensure
switch opens at 170-218 psi (12-15 kg/cm2 ) . Difference between opening and closing points must be at least
29.0 psi (2.04 kg/cm2 ) . Switch can be removed without discharging system.

HIGH PRESSURE CUT-OUT SWITCH

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Switch is identified by Red housing and located on right/left side of condenser. Cut-out switch turns off A/C
compressor clutch when refrigerant pressure reaches 409.0-450.0 psi (28.76-31.60 kg/cm2 ) . Switch can be
replaced without discharging system. Ensure switch closes at 149.0-250.0 psi (10.45-17.58 kg/cm2 ) . Replace
switch if necessary.

IN-CAR TEMPERATURE SENSORS

In-car temperature sensors measure interior air temperature and send signals to A/C-heater control panel. A
small fan drives air over instrument panel sensor to ensure accurate measurement. One sensor is mounted on top
of instrument panel, and a second sensor is located next to front dome light.

LOW PRESSURE SWITCH

Refrigerant low pressure switch disengages A/C compressor clutch if refrigerant pressure drops below specified
pressure. Ensure switch opens at 21.0-23.0 psi (1.48-1.62 kg/cm2 ) . Ensure switch closes at 42.0-49.0 psi (2.95-
3.45 kg/cm2 ) . Replace switch if necessary.

TWO-WAY VACUUM VALVES

Fresh/Recirculated Air Flap

This two-way vacuum valve is used to control vacuum applied to fresh/recirculated air flap door vacuum servo.
Valve is located on left side of evaporator assembly, in air plenum.

Two-way vacuum valve is controlled by signals from A/C-heater control panel. When vacuum is applied to
fresh/recirculated air flap door vacuum servo, flap door closes and no fresh air enters vehicle.

Heater Control (Coolant) Valve

This vacuum valve is located on right side of heater box, in air plenum. See Fig. 2 . Two-way vacuum valve is
electrically controlled by signals from A/C-heater control panel, which directs or vents vacuum to heater control
valve. When vacuum is applied to heater control valve, no coolant flows through heater core.

SELF-DIAGNOSTICS

NOTE: Scan Tester (VAG 1551) must be used to make full use of the system's self-
diagnostic capabilities.

The complete self-diagnostics functions and operating instructions of VAG 1551 scan tester are not covered.
Follow VAG 1551 operator's manual and accompanying trouble shooting manual. The following text highlights
functions available when using VAG 1551 scan tester.

DIAGNOSTIC TROUBLE CODE MEMORY

NOTE: Diagnostic trouble code memory is cleared when ignition is turned off. DO NOT

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turn ignition off after driving vehicle, as this will erase fault codes.

If a malfunction occurs in a monitored sensor or component, a Diagnostic Trouble Code (DTC) is stored in
memory. This function may be used by technician to access and erase DTCs. Codes may be either hard or
intermittent failures.

Hard Failures

If A/C-heater system malfunctions are present for more than 5 seconds, they are stored as Diagnostic Trouble
Codes (DTCs). The A/C compressor control module distinguishes data between 19 different trouble codes and
stores malfunctions until ignition is turned off (volatile memory).

Intermittent Failures

If malfunction occurs intermittently, they are stored and considered to be "sporadic" (intermittent) failures.
When displayed on scan tester, intermittent malfunctions will have "SP" (sporadic) on right side of display.

MEASURING VALUE BLOCK

Ten measuring value blocks, with 4 measuring channels each, are used. Monitored sensors and components
include A/C compressor switch-off conditions, temperature regulator flap motor, central flap motor,
footwell/defroster flap motor, airflow flap motor, and motor potentiometers.

Measuring value block function monitoring includes display and measuring values of all ambient, fresh air
intake duct, and in-car temperature sensors. Voltage at fresh air blower, engine speed, A/C compressor speed,
and vehicle speed are monitored. Inputs from Engine Coolant Temperature (ECT) sensor, kick-down switch,
A/C compressor engagement, and A/C high pressure switch are also monitored.

OUTPUT DIAGNOSTIC TEST MODE

Since VAG 1551 scan tester is a bi-directional tester, it may be used to actuate a number of A/C-heater system
components. The output diagnostic test mode may be used to actuate A/C compressor clutch, fresh air blower,
temperature sensor blower fan, and cooling fan.

The A/C-heater control panel segment displays, outside temperature indicator (display), and Idle Air Control
(IAC) may also be actuated.

In addition, temperature regulator flap motor, central flap motor, footwell/defroster flap motor, airflow flap
motor, and fresh/recirculated air flap two-way valve may also be actuated.

A/C CONTROL HEAD CODING

Replacement A/C control heads (A/C-heater control panel) are sold with Code 000 and must be properly coded
after installation. Contact nearest Audi parts department to determine correct application.

ON-BOARD DIAGNOSTICS (OBD)

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HEAT, VENTILATION & A/C 1995-96 Auto. A/C-Heater Systems

NOTE: While OBD information is being displayed on A/C-heater control panel, A/C
system operation does not take place (A/C compressor, radiator fan, etc. are not
controlled).

ACCESSING MEMORY DIAGNOSTIC CHANNELS

1. Turn ignition switch on or start engine. Simultaneously press and hold down air recirculation button and
air distribution (up arrow) button. See Fig. 1 . Release both buttons. Display panel should read "01c",
indicating diagnostic channel No. 1.
2. Pressing temperature plus (+) button will advance display of diagnostic channel by one. Display panel
should read "02c", indicating diagnostic channel No. 2. Each time plus (+) button is pressed, system will
advance to next diagnostic channel until last number is reached; display will then return to channel No. 1.
3. Memory diagnostic channels identify individual circuits, and are not fault codes. See MEMORY
DIAGNOSTIC CHANNELS table. To retrieve information about a particular channel, select desired
channel then press air recirculation button.
4. If channel No. 52 is selected and A/C compressor switch-off condition exists, a segment of "88.8" display
will illuminate indicating cause of condition. See Fig. 4 .
5. Channel No. 53 is used to identify which A/C electrical components (outputs) are activated. When
channel No. 53 is selected, a segment of "88.8" display will illuminate. See Fig. 4 .
6. On both channels No. 52 and 53, segments 7, 14 and 21 of "88.8" display must illuminate simultaneously
to indicate system function is okay. See Fig. 4 .

EXITING ON-BOARD DIAGNOSTICS

To exit memory diagnostic channel display, press AUTO button or turn ignition off.

MEMORY DIAGNOSTIC CHANNELS

Diagnostic Channel No. Display
1 System Malfunction Displayed As Diagnostic
Trouble Code (See DIAGNOSTIC TROUBLE
CODES table)
2 Digital Value Of In-Car Temperature Sensor
(Headliner) Digital Value Of In-Car Temperature
Sensor (Instrument Panel)
4 Digital Value Of Fresh Air Intake Duct Temperature
Sensor
5 Digital Value Of Outside (Ambient) Temperature
Sensor (Front)
6 Digital Value Of Outside (Ambient) Temperature
Sensor
7 Digital Value Of Ambient Temperature Sensor At
Fresh Air Blower
8 Digital Value Of Temperature Regulator Flap Motor
Potentiometer
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9 Delta Value Of Temperature Regulator Flap

10 Non-Corrected Specified Value Of Temperature
Regulator Flap
11 Digital Value Of Central Flap Motor Potentiometer
12 Specified Value Of Central Flap
13 Digital Value Of Footwell/Defroster Flap Motor
Potentiometer
14 Specified Value Of Footwell/Defroster Flap
15 Digital Value Of Airflow Flap Motor Potentiometer
16 Specified Value Of Airflow Flap
17 Vehicle Speed (Kilometers Per Hour)
18 Actual Fresh Air Blower Voltage
19 Specified Fresh Air Blower Voltage
20 A/C Compressor Clutch Voltage
21 Number Of Low Voltage Occurrences (Non-
Transient)
22 Cycle Condition Of A/C Refrigerant High Pressure
Cut-Out Switch
23 Cycling Of A/C Refrigerant High Pressure Cut-Out
Switch
24 Cycling Of Switches, Absolute & Non-Fluctuating
25 Kick-Down Switch Analog/Digital Value
26 Engine Coolant Temperature (ECT) Sensor
Warning Light Analog/Digital Value
27 Coding Value
28 Engine Speed (RPM)
29 (1) A/C Compressor Speed In RPM (Equals Engine
Speed x 1.28)
30 Software Version
31 Segment Display Check (All Segments Of A/C-
Heater Control Panel Light Up)
32 Temperature Regulator Flap Potentiometer
Malfunction Counter
33 Central Flap Potentiometer Malfunction Counter
34 Footwell/Defroster Flap Potentiometer Malfunction
Counter
35 Airflow Flap Potentiometer Malfunction Counter
36 Temperature Regulator Flap Motor Potentiometer
Feedback Value (Cold End Stop)
37 Temperature Regulator Flap Motor Potentiometer
Feedback Value (Hot End Stop)
38 Central Flap Motor Potentiometer Feedback Value

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(Cold End Stop)

39 Central Flap Motor Potentiometer Feedback Value
(Hot End Stop)
40 Footwell/Defroster Flap Motor Potentiometer
Feedback Value (Cold End Stop)
41 Footwell/Defroster Flap Motor Potentiometer
Feedback Value (Hot End Stop)
42 Airflow Flap Motor Potentiometer Feedback Value
(Cold End Stop)
43 Airflow Flap Motor Potentiometer Feedback Value
(Hot End Stop)
44 Vehicle Operation Cycle Counter
45 Calculated Interior Temperature, In Digits (Internal
Software)
46 Outside (Ambient) Temperature, Filtered For
Regulation (Internal Software)
47 Outside (Ambient) Temperature, Unfiltered In
Degrees °C (Internal Software)
48 Outside (Ambient) Temperature, Unfiltered In
Digits
49 Malfunction Counter For Speedometer (Vehicle
Speed) Signal
50 Standing Time (In Minutes)
51 Engine Coolant Temperature (ECT) In Degrees °C
52 (2) Graphics Channel Number 1 - 88.8 Display
53 (2)
Graphics Channel Number 2 - 88.8 Display
54 Control Characteristics
55 Outside (Ambient) Temperature, In Degrees °F Or °
C, Depending On A/C-Heater Control Panel Setting
56 In-Car Temperature Sensor Temperature In Degrees
°C (Headliner)
57 In-Car Temperature Sensor Temperature In Degrees
°C (Instrument Panel)
58 Fresh Air Duct Temperature Sensor Temperature In
Degrees °C
59 Front Outside (Ambient) Temperature Sensor
Temperature In Degrees °C
60 Fresh Air Blower Ambient Temperature Sensor
Temperature In Degrees °C
61 Software Version (Latest)
(1) Not applicable to vehicles equipped with a Nippondenso compressor.

(2) When diagnostic channel No. 52 or 53 is selected, "_ _ . _" is displayed first. The A/C compressor

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switch-off conditions are identified by the illuminated segments of display. See Fig. 4 .

Fig. 4: Identifying Diagnostic Channel No. 52 & 53

Courtesy of AUDI OF AMERICA, INC.

RETRIEVING & CLEARING FAULT CODES

1. To retrieve fault codes using A/C-heater control panel, access memory diagnostic channels. See ON-
BOARD DIAGNOSTICS (OBD) . If a diagnostic fault code exists, fault code will be displayed in
channel No. 1. If no fault code exists, "00.0" will be displayed.
2. If a fault code exists, repair malfunction indicated. See DIAGNOSTIC TROUBLE CODES table. After
malfunction is corrected, clear diagnostic trouble codes. To clear codes, VAG 1551 must be used.

DIAGNOSTIC TROUBLE CODES

Diagnostic Trouble Code Affected Circuit
00.0 No Malfunctions

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02.1-02.4 In-Car Temp. Sensor (Headliner)

03.1-03.4 In-Car Temp. Sensor (Instrument Panel)
04.1-04.4 Fresh Air Intake Duct Temp. Sensor
05.1-05.4 Outside (Ambient) Temp. Sensor (Front)
06.1-06.4 Engine Coolant Temp. (ECT) Sensor
07.1-07.4 Fresh Air Blower Ambient Temp. Sensor
08.1-08.7 (1) Temp. Regulator Flap Motor Potentiometer
11-1-11.7 (1) Central Flap Motor Potentiometer
13.1-13.7 (1) Footwell/Defroster Flap Motor Potentiometer
15.1-15.7 Airflow Flap Motor Potentiometer
17.0 Vehicle Speed Signal
18.1-18.3 Fresh Air Blower (Incorrect Voltage)
20.1-20.3 (2) A/C Compressor (Incorrect Voltage)
22.1-22.5 (3) A/C High Pressure Cut-Out Switch
29.1-29.4 A/C Belt Slip
(1) Motors will no longer be controlled automatically.

(2) The A/C compressor remains off until voltage is greater than 10.8 volts for at least 25 seconds.
(3) The A/C compressor remains off until switch closes.

TESTING

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 RESTRAINT SYSTEM article in
ACCESSORIES/SAFETY EQUIPMENT SECTION.

A/C SYSTEM PERFORMANCE

1. Park vehicle out of direct sunlight. Ensure condenser and radiator are free of obstructions. Ensure
compressor drive belt is in good condition. Ensure engine is at normal operating temperature. Close
engine hood.
2. Start engine and run it at 2000 RPM. Turn A/C system on and press AUTO mode button. See Fig. 1 .
Press minus (-) button until "LO" temperature setting is displayed.
3. Press air recirculation button until recirculated air symbol is displayed. Press compressor on/off button
until ice crystal symbol is displayed. See Fig. 1 .
4. Open all instrument panel air outlets. Ensure cooling fan and A/C compressor run. Ensure blower motor
runs on high speed and air flows out of instrument panel vents.
5. Using VAG 1551 scan tester, check DTC memory. Close doors, windows, and sun roof. Record ambient
temperature and check outlet air temperature at center instrument panel vent after A/C system has run for
5 minutes. See A/C SYSTEM PERFORMANCE SPECIFICATIONS table.
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NOTE: If A/C compressor clutch disengages during performance test, go to step

11).

A/C SYSTEM PERFORMANCE SPECIFICATIONS

Ambient Temp. °F (°C) Outlet Air Temp. °F (°C)
59 (15) 37-43 (3-6)
68 (20) 37-43 (3-6)
77 (25) 37-43 (3-6)
86 (30) 37-43 (3-6)
95 (35) 39-45 (4-7)
104 (40) 41-48 (5-8)

6. If outlet air temperature is not as specified, remove low pressure switch and jumper connector terminals.
Remove high pressure switch, leaving its wiring harness connected. Connect manifold gauge set to high
and low pressure service valves.
7. Repeat A/C system performance test. High side (discharge) pressure should increase from base pressure
(engine off) to a maximum of 290 psi (20.4 kg/cm2 ) . See A/C SYSTEM BASE (HIGH SIDE)
PRESSURE SPECIFICATIONS table.
8. The high pressure switch should switch cooling fan to second speed between 190-254 psi (13.4-17.9
kg/cm2 ) . If cooling fan does not switch to second speed, check cooling fan circuit.
9. The low side (suction) pressure should be as specified in A/C SYSTEM LOW SIDE PRESSURE
SPECIFICATIONS table. If both high and low side pressures are okay, A/C system cooling
performance is okay. Check low pressure and high pressure switches as necessary.
10. If either high or low side pressures are incorrect, check refrigerant and A/C system for malfunctions (low
refrigerant charge, faulty compressor, kinked/plugged A/C hose, etc.).

A/C SYSTEM BASE (HIGH SIDE) PRESSURE SPECIFICATIONS

Ambient Temp. °F (°C) (1) psi (kg/cm2 )
59 (15) 56.6 (3.9)
68 (20) 68.2 (4.7)
77 (25) 81.2 (5.6)
86 (30) 97.2 (6.7)
95 (35) 113.1 (7.8)
104 (40) 132.0 (9.1)
113 (45) 152.3 (10.5)
(1) Pressures listed are with engine off.

A/C SYSTEM LOW SIDE PRESSURE SPECIFICATIONS

Ambient Temp. °F (°C) Pressure psi (kg/cm2 )
50 (10) 30-32 (2.1-2.2)
59 (15) 29-32 (2.0-2.2)
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68 (20) 28-30 (1.9-2.1)

77 (25) 26-29 (1.8-2.0)
86 (30) 25-29 (1.7-2.0)
95 (35) 25-30 (1.7-2.1)
104 (40) 28-33 (1.9-2.3)

11. Check Diagnostic Trouble Code (DTC) memory. See DIAGNOSTIC TROUBLE CODE MEMORY
under SELF-DIAGNOSTICS. Repair A/C system malfunctions (if any). Erase DTC memory. End session
using RAPID DATA TRANSFER, leaving VAG 1551 connected. Repeat A/C system performance test.
12. Ensure scan tester is in A/C/HEATING ELECTRONICS function. With RAPID DATA TRANSFER
displayed on scan tester, press "0" and "8" buttons to select READ MEASURING VALUE BLOCK
function. Press "Q" button to enter input.
13. With INPUT DISPLAY GROUP NUMBER displayed on scan tester, press "0" and "1" buttons to select
COMPRESSOR SWITCH-OFF CONDITIONS. Press "Q" button to enter input.
14. Read display group No. 1, channel No. 1. If Code 2 (high pressure cut-out switch) is displayed, go to next
step. If Code 3 (low pressure switch) is displayed, go to step 20). If other codes are displayed, go to
MEASURING VALUE BLOCK under SELF-DIAGNOSTICS.
15. End session using RAPID DATA TRANSFER. Remove high pressure cut-out switch, leaving its wiring
harness connected. Connect manifold gauge set to high pressure cut-out switch Schrader valve.
16. Repeat A/C system performance test and check A/C system high side pressure. High side (discharge)
pressure should increase from base pressure (engine off) to a maximum of 290 psi (20.4 kg/cm2 ) . See
A/C SYSTEM BASE (HIGH SIDE) PRESSURE SPECIFICATIONS table.
17. The high pressure switch should switch cooling fan to second speed between 190-254 psi (13.4-17.9
kg/cm2 ) . If cooling fan does not switch to second speed, check cooling fan circuit.
18. If required cooling performance is attained and no other malfunction is detected, replace high pressure
cut-out switch. If high side pressure is exceeded, check refrigerant and A/C system for malfunctions.
19. If A/C compressor clutch still does not engage, check wiring harness between A/C control panel and high
pressure cut-out switch. Repair wiring harness as necessary.
20. End session using RAPID DATA TRANSFER. Remove low pressure switch and jumper connector
terminals. Connect manifold gauge set to low pressure switch Schrader valve.
21. Repeat A/C system performance test and check A/C system low side pressure. Low side (suction)
pressure should be as specified in A/C SYSTEM LOW SIDE PRESSURE SPECIFICATIONS table.
22. If required cooling performance is attained and no other malfunction is detected, replace low pressure
switch. If low side pressure is incorrect, check refrigerant and A/C system for malfunctions (low
refrigerant charge, faulty A/C compressor, kinked/plugged A/C hose, etc.).
23. If A/C compressor clutch disengages during test, check wiring harness between A/C control panel and
low pressure switch. Repair wiring harness as necessary.
24. If A/C compressor clutch does not disengage during test, check heater box and evaporator assembly for
air leaks. If no leaks are found, A/C system may be low on refrigerant. Check refrigerant lines and
components for leaks. Repair leaks as necessary.

ACTUATORS, SENSORS & FAN CONTROL MODULE

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NOTE: Manufacturer recommends the use of VAG 1551 scan tester for circuit and
component testing.

AUTOMATIC A/C-HEATER SYSTEM COMPONENT TESTING

Component Being Tested (VAG Test Condition Resistance Voltage Value
1598 Pin No.)
In-Car Temp. Sensor Headliner 43 Ambient Temp. At Sensor (2) 3513 Ohms @ 68°F (20°C)
& 52 (1)

In-Car Temp. Sensor Dash (50 & (3) Ambient Temp. At Sensor (2) 3513 Ohms @ 68°F (20°C)
52 )(1)

Fresh Air Temp. Sensor (47 & 52 Ambient Temp At Sensor (2) 1250 Ohms @ 68°F (20°C)
(1) )

Ambient Temp. Sensor (48 & 52 Ambient Temp. At Sensor (2) 1250 Ohms @ 68°F (20°C)
(1) )

Temp. Regulator Flap Motor (2 & - 20-100 Ohms

10 )(4)

Central Air Distribution Flap - 20-100 Ohms

Motor (4 & 12 ) (4)

Footwell/Defroster Flap Motor (3 - 20-100 Ohms

& 11 ) (4)

Fan Control Module (16 & Ignition On Less Than 0.5 Volt (Blower Motor
Ground ) (5) Off)
Blower Motor Voltage Supply (14 Ignition On Battery Voltage
& Ground ) (5)

Fan Control Module Voltage Ignition On Battery Voltage

Supply (11 & Ground ) (5)

Fan Control Module (13 & 16 (6) ) Ignition On LED Tester Lights Up (Blower
Motor On)
(1) Connect Adapter Harness (VAG 1598/11) to Test Box (VAG 1598). See DVOM to 20,000-ohm
range.
(2) See AMBIENT, IN-CAR & FRESH AIR TEMPERATURE SENSOR RESISTANCE VALUES
table for complete temperature range specifications.
(3) Check temperature sensor fan using diagnostic test mode. See OUTPUT DIAGNOSTIC TEST
MODE under SELF-DIAGNOSTICS.
(4) Connect Adapter Harness (VAG 1598/12) to Test Box (VAG 1598). Set DVOM to 200-ohm range.

(5) Connect Adapter Harness (VAG 1598/11) to Test Box (VAG 1598). Set DVOM to 20-volt range.
(6) Connect Adapter Harness (VAG 1598/11) to Test Box (VAG 1598) and use LED Tester (US 1115).

AMBIENT, IN-CAR & FRESH AIR TEMPERATURE SENSOR RESISTANCE VALUES

Ambient & Fresh Air Temp.
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HEAT, VENTILATION & A/C 1995-96 Auto. A/C-Heater Systems

Temp. °F (°C) At Sensor Sensors (Ohms) In-Car Temp. Sensors (Ohms)

14 (-10) 5591 16,159
32 (0) 3281 9406
41 (5) 2544 7273
50 (10) 1991 5666
59 (15) 1571 4446
68 (20) 1250 3513
77 (25) 998 2795
86 (30) 804 2237
95 (35) 652 1801
104 (40) 533 1459
113 (45) 437 1188
122 (50) 361 972
131 (55) 300 803
140 (60) 250 667
149 (65) n/a 556
158 (70) n/a 466

REMOVAL & INSTALLATION

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 RESTRAINT SYSTEM article in
ACCESSORIES/SAFETY EQUIPMENT SECTION.

A/C COMPRESSOR

Removal & Installation

1. Discharge A/C system, using approved refrigerant recovery/recycling equipment. Mark direction of drive
belt. Loosen drive belt tensioner and remove drive belt. Remove bracket for refrigerant line. Remove
bolts and A/C compressor. Remove and plug high and low pressure lines from A/C compressor.
2. To install, reverse removal procedure. Tighten connections to specification. See TORQUE
SPECIFICATIONS table. Evacuate and charge A/C system.

A/C COMPRESSOR SPEED SENSOR

Removal & Installation (Zexel Compressors)

Discharge A/C system, using approved refrigerant recovery/recycling equipment. Disconnect speed sensor
connector. Remove screws and sensor. To install, reverse removal procedure. Tighten screws to specification.
See TORQUE SPECIFICATIONS table.

A/C-HEATER CONTROL PANEL

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HEAT, VENTILATION & A/C 1995-96 Auto. A/C-Heater Systems

NOTE: Before removing A/C-heater control panel, check for codes. See SELF-
DIAGNOSTICS .

Removal & Installation

Turn ignition off. Carefully pry off A/C-heater control panel trim. Remove screws and A/C-heater control
panel. To install, reverse the removal procedure. Tighten screws to proper specification. See TORQUE
SPECIFICATIONS table.

ACTUATORS

Removal & Installation

1. To remove fresh air/recirculating flap vacuum motor, remove plenum tray. Rotate vacuum motor 90
degrees, and pull from mount. Disconnect vacuum hose, and secure aside. DO NOT allow vacuum hose
to slide into evaporator housing. Remove fresh air/recirculating flap motor (vacuum servo).
2. To remove temperature regulator flap motor, remove plenum tray. Entirely remove windshield wiper
motor and linkage assembly. Remove cover and temperature regulator flap motor.
3. To remove central flap and footwell/defroster flap motor, remove center console. See CENTER
CONSOLE . Remove glove box and driver's side tray. Remove defroster hoses from left and right sides
of heater box.
4. Remove central flap and footwell/defroster flap motor support tray screws from left and right sides of
heater box. Disconnect wiring harness Blue connector at central flap motor. See Fig. 5 .
5. Disconnect wiring harness Red connector at footwell/defroster flap motor. Remove central flap and
footwell/defroster flap motor support tray. Remove motor(s) from support tray. To install, reverse
removal procedure.

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HEAT, VENTILATION & A/C 1995-96 Auto. A/C-Heater Systems

Fig. 5: Removing Footwell/Defroster & Central Flap Motors

Courtesy of AUDI OF AMERICA, INC.

CENTER CONSOLE
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 1996 Audi A6 Quattro
HEAT, VENTILATION & A/C 1995-96 Auto. A/C-Heater Systems

Removal & Installation (Rear)

1. Obtain radio anti-theft protection code. Disconnect negative battery cable. Unscrew and remove gearshift
knob. Disengage gearshift lever trim from retaining clip. Remove gearshift lever trim.
2. Unclip cigarette trim plate, and remove self-tapping screws. Lift up lining, and remove self-tapping
screw. Pull out rear air duct and disconnect electrical connectors. Remove rear air duct.
3. Slide driver's and passenger's seats fully forward. Pull parking brake lever up as far as possible. Carefully
pry handle from parking brake lever. Remove screws and clip securing front of console. Remove bolts
securing rear center console. Remove rear center console. To install, reverse removal procedure.

NOTE: Front center console can be removed without removing center section of
instrument panel.

Removal & Installation (Front)

Remove rear center console. Unclip cover and remove nut. Remove radio. Pull out center air outlet, and remove
bolts. Remove trim plates. Remove bolts and ashtray. Loosen bolts at front of console. Remove front center
console. To install, reverse removal procedure.

EVAPORATOR

Removal & Installation

1. Discharge A/C system, using approved refrigerant recovery/recycling equipment. Remove glove box.
Remove 4 evaporator cover bolts. Remove plenum tray. Disconnect and plug refrigerant lines. Disconnect
evaporator housing electrical connections. Remove evaporator housing.
2. To install, reverse removal procedure. Use NEW seal between evaporator and firewall. Use NEW "O"
rings. Tighten connections to specification. See TORQUE SPECIFICATIONS table. Ensure water
drain hose connections and tightly sealed, and hose is not kinked. Ensure water drain valve operates
properly. Ensure no air leaks exist.

FRESH AIR BLOWER

Removal & Installation

Remove plenum tray. Remove heater box. See HEATER BOX . Remove intake duct with fresh air flap.
Remove locking clip, retaining washer and grommet. To install, reverse removal procedure. Lubricate mounting
tabs with petroleum jelly.

FRESH AIR BLOWER CONTROL MODULE

Removal & Installation

Remove glove box. Disconnect wiring harness connector from fan control (fresh air blower) control module.
Carefully remove fan control module (heat sink may be hot). To install, reverse removal procedure.

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 1996 Audi A6 Quattro
HEAT, VENTILATION & A/C 1995-96 Auto. A/C-Heater Systems

FRESH AIR TEMPERATURE SENSOR

Removal & Installation

Remove right side plenum tray. Remove fresh air intake duct grille. Remove glove box. Twist temperature
sensor, and remove from fresh air duct. To install sensor, spray sensor seal with silicone. Reverse removal
procedure to complete installation.

HEATER BOX

NOTE: Heater box can be removed without discharging A/C system.

Removal

1. Remove plenum tray. Remove wiper motor/linkage assembly. Remove center console. See CENTER
CONSOLE . Remove glove box and driver's side tray. Remove footwell air outlet on driver's and
passenger's side.
2. Remove rubber coupling between evaporator housing and heater box. Remove hoses and connecting
bellows to rear heater duct. Remove connections between heater box and evaporator housing. Loosen cap
on coolant expansion tank. Disconnect coolant hoses from heater box. Remove screw and tensioning
strap.
3. Disconnect heater box electrical connections. Attach Engine Support Bridge (10-222 A/1) and Heater
Claw (2075) to lip of heater box. Tighten nut on engine support bridge to loosen heater box. Remove
engine support bridge and heater claw. Remove heater box.

Installation

To install, reverse removal procedure. Replace adhesive sealing tape, positioning sealing tape ends at top of
heater box. Check rubber coupling for leaks. When assembling housing, apply silicon rubber to area of housing
above temperature flap.

HEATER CONTROL (COOLANT) VALVE

Removal & Installation

Remove plenum tray. Loosen coolant expansion tank cap to relieve pressure. Disconnect coolant hoses from
heater core. Plug coolant hoses to prevent contamination. Remove coolant hoses from valve. Remove screw and
heater control valve. To install, reverse removal procedure.

IN-CAR TEMPERATURE SENSOR

Removal & Installation

Remove glove box. Disconnect hose and wiring harness from sensor. Remove screws and in-car temperature
sensor. To install, reverse removal procedure. Ensure hose is securely attached.

INSTRUMENT CLUSTER
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 1996 Audi A6 Quattro
HEAT, VENTILATION & A/C 1995-96 Auto. A/C-Heater Systems

Removal & Installation

Remove rear and front center consoles. See CENTER CONSOLE . Remove center section of instrument
panel. Remove steering wheel. Remove steering column switch. Remove bolts and trim strip. Remove screws
and instrument cluster. To install, reverse removal procedure.

ORIFICE TUBE

Removal & Installation

1. Discharge A/C system, using approved refrigerant recovery/recycling equipment. Loosen refrigerant line
clamp and remove lines from evaporator. Using needle nose pliers, remove restrictor (orifice tube) from
evaporator inlet. Plug openings to prevent contamination.
2. To install, reverse removal procedure. Use NEW "O" rings. Insert orifice tube with arrow pointing
toward evaporator, and push until firmly seated.

TORQUE SPECIFICATIONS
TORQUE SPECIFICATIONS
Application Ft. Lbs. (N.m)
A/C Compressor Bolts 18 (25)
A/C Compressor Bracket Bolts 18 (25)
A/C Compressor High Pressure Connection 22 (30)
A/C Compressor Low Pressure Connection 30 (40)
Accumulator Lines 30 (40)
Condenser
Inlet Line 22 (30)
Outlet Line 11 (15)
Evaporator
Inlet Line 11 (15)
Outlet Line 30 (40)
Refrigerant Line Clamp Bolt 11 (15)
INCH Lbs. (N.m)
A/C Compressor Speed Sensor 44 (5)
Compressor Oil Drain Plug 89 (10)
Compressor Pressure Relief Valve 89 (10)
Heater Controls Trim Plate Screws 18 (2)
High Pressure Cut-Out Switch (1) 44 (5)
High Pressure Switch (1) 44 (5)
Low Pressure Switch (1) 44 (5)
(1) High pressure switch, high pressure cut-out switch, and low pressure switch may be removed without
discharging A/C system.

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 1996 Audi A6 Quattro
HEAT, VENTILATION & A/C 1995-96 Auto. A/C-Heater Systems

WIRING DIAGRAMS

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 1996 Audi A6 Quattro
HEAT, VENTILATION & A/C 1995-96 Auto. A/C-Heater Systems

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 1996 Audi A6 Quattro
HEAT, VENTILATION & A/C 1995-96 Auto. A/C-Heater Systems

Fig. 6: A/C-Heater System Wiring Diagram (Early 95 Prod'n - 1 Of 2)

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 1996 Audi A6 Quattro
HEAT, VENTILATION & A/C 1995-96 Auto. A/C-Heater Systems

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 1996 Audi A6 Quattro
HEAT, VENTILATION & A/C 1995-96 Auto. A/C-Heater Systems

Fig. 7: A/C-Heater System Wiring Diagram (Early 95 Prod'n - 2 Of 2)

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 1996 Audi A6 Quattro
HEAT, VENTILATION & A/C 1995-96 Auto. A/C-Heater Systems

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 1996 Audi A6 Quattro
HEAT, VENTILATION & A/C 1995-96 Auto. A/C-Heater Systems

Fig. 8: A/C-Heater System Wiring Diagram (Late 95 Prod'n/96 1 Of 2)

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 1996 Audi A6 Quattro
HEAT, VENTILATION & A/C 1995-96 Auto. A/C-Heater Systems

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 1996 Audi A6 Quattro
HEAT, VENTILATION & A/C 1995-96 Auto. A/C-Heater Systems

Fig. 9: A/C-Heater System Wiring Diagram (Late 95 Prod'/96 - 2 Of 2)

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