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Air Conditioning: Diagnosis Audi A8 D2 facelift

Automatic HVAC System 7 illustrations ~1726 words

Testing

  1. Start engine. Compressor switched on (AUTO mode selected)

If the compressor is activated

  1. Disconnect harness connector -B- from switch. Compressor will stop (low pressure switch open).
  2. Remove switch -A- and install harness connector -B-. Compressor will not be activated (low pressure switch open).

If the compressor is not activated

  1. Disconnect harness connector -B- from switch -A- and bridge terminals -1- and -2- on harness connector -B-. The compressor will be activated.

Note. If the compressor is activated when the terminals are connected together, either the pressure in the A/C system is too low (A/C system empty), or the switch is malfunctioning. Check the pressure in the refrigerant circuit. See A/C REFRIGERANT SYSTEM (R-134A), CHECKING PRESSURES . If the compressor is not activated and the measuring value block display indicates A/C pressure switch -F129- as the cut-off condition, find and repair the open circuit in the wiring between A/C pressure switch -F129- and A/C control head -E87-.

Test requirements

  1. Vehicle is in an area where there is clean recirculating air (not near running engines, openings from exhaust systems, etc.)
  2. Engine compartment and plenum chamber are clean (not contaminated with oil and/or fuel)
  3. The engine compartment and plenum chamber were not sprayed with cleaning or preservative solutions
  1. Radiator and condenser are clean (clean, if necessary)
  2. Ribbed V-belt is in proper order and correctly tensioned
  3. All air guides, covers and seals in proper order and correctly installed
  4. Air flow through the two dust and pollen filters not restricted
  5. The vehicle is not directly exposed to the sun's rays
  6. Engine is at normal operating temperature With engine running, select the following A/C control head - E87- settings. "Auto" mode for driver and passenger sides "ECON" button not switched on (compressor switched on) "LO" temperature selection (driver and passenger sides)
  7. A/C compressor is driven (the A/C clutch is switched on)
  8. Radiator coolant fan -V7- runs (at least in stage 1).
  9. Fresh air blower -V2- runs at maximum speed.
  10. The air flow flap closes and recirculating air flap opens (about 1 minute after engine is started).
  11. The coolant pump -V50- does not run.
  12. Both left and right heat regulating valves (-N175- and - N176-) are closed (coolant hoses and coolant hoses to the heating system heater cores cool down).

Note. Testing heating performance of A/C system and operation of pump valve unit. See AUTOMATIC CLIMATE CONTROL SYSTEM HEATING PERFORMANCE AND OPERATION OF PUMP VALVE UNIT, TESTING . If one of the test requirements is not achieved, check DTC memory and perform output Diagnostic Test Mode (DTM). See OUTPUT DIAGNOSTIC TEST MODE (DTM) (FUNCTION 03) .

  1. Switch ignition on.
  2. Open center instrument panel air outlets.
  3. Position thumb wheel for temperature-controlled center outlet to "warm".
  4. Set operating mode to "Auto" and "LO" temperature selection for driver and passenger sides on A/C control head - E87-.
  5. Start engine (compressor is operated).
  6. Run engine at 2000 RPM (start of time measurement).
  7. Measure temperature of air flowing out of the center instrument panel air outlets (driver and passenger sides).

Compare measurements with the diagram.

Note. If the specified values are not achieved. See DETERMINING MALFUNCTION IF TEST RESULTS DIFFER FROM SPECIFICATIONS . It is good practice to use two separate thermometers for this measurement. The temperature of the air in the mixing chambers of the air conditioner housing (downstream of heater core) can be measured with VAG 1551 during the A/C system cooling performance test (Read measuring value block, function 08. See READ MEASURING VALUE BLOCK (FUNCTION 08) , display group 014).

Scheme 1

Scheme 1
Scheme 1

Scheme 2

Scheme 2: Determining malfunction if test results differ from specifications
Scheme 2: Determining malfunction if test results differ from specifications
  1. To repeat A/C system cooling performance test, see «TESTING»(ref-196891-S23758350142005101000000) .
  2. For repairing possible malfunctions in refrigerant system, see «A/C REFRIGERANT SYSTEM (R-134A), CHECKING PRESSURES»(ref-196891-S41270873522005101000000) .
  1. Test actuation of left and right heat regulating valves -N175- and -N176-, as well as coolant pump -V50-. See «AUTOMATIC CLIMATE CONTROL SYSTEM HEATING PERFORMANCE AND OPERATION OF PUMP VALVE UNIT, TESTING»(ref-196891-S25458045492005101000000) .

Scheme 3

Scheme 3
Scheme 3
  1. To perform electrical test, see «AUTOMATIC CLIMATE CONTROL SYSTEM, ELECTRICAL TESTS»(ref-196890-S20846794822005101000000) .
  2. To repeat A/C system cooling performance test, see «TESTING»(ref-196891-S23758350142005101000000) .
  1. Check DTC memory with VAG 1551 Scan Tool, determine and repair all the malfunctions displayed. See «DIAGNOSTIC TROUBLE CODE (DTC) MEMORY, CHECKING (FUNCTION 02)»(ref-196890-S16133676342005101000000) .
  2. Erase DTC memory. See «DIAGNOSTIC TROUBLE CODE (DTC) MEMORY, ERASING (FUNCTION 05)»(ref-196890-S22847116632005101000000) .
  3. Start engine.
  4. Read measured value block, function 08. See «READ MEASURING VALUE BLOCK (FUNCTION 08)»(ref-196890-S05680158692005101000000) .
  5. Select display group 001 and confirm entry with -Q- button.
  6. Repeat cooling performance test. See «TESTING»(ref-196891-S23758350142005101000000) and monitor display field 1 on VAG 1551.

Scheme 4

Scheme 4
Scheme 4
  1. To read measuring value block, display group 001, see «READ MEASURING VALUE BLOCK (FUNCTION 08)»(ref-196890-S05680158692005101000000) .

Scheme 5

Scheme 5
Scheme 5
  1. To check pressures in A/C refrigerant system, see «A/C REFRIGERANT SYSTEM (R-134A), CHECKING PRESSURES»(ref-196891-S41270873522005101000000) .
  2. To perform A/C system cooling performance test, see «TESTING»(ref-196891-S23758350142005101000000) .
  3. To unplug connector to high pressure switch F23 and bridge connector terminals 1 and 2, see «A/C refrigerant high pressure switches -F23- and -F118»(ref-196891-S06674014302005101000000) .
  1. Unplug connector from the A/C refrigerant low pressure switch - F73- and bridge the two terminals of the connector.
  2. Check pressures in refrigerant system. See «A/C REFRIGERANT SYSTEM (R-134A), CHECKING pressures»(ref-196891-S41270873522005101000000) .
  3. Repeat A/C system cooling performance test. See «TESTING»(ref-196891-S23758350142005101000000) .

Scheme 6

Scheme 6
Scheme 6
  1. To check pressures in A/C refrigerant system, see «A/C REFRIGERANT SYSTEM (R-134A), CHECKING PRESSURES»(ref-196891-S41270873522005101000000) .
  2. To perform A/C system cooling performance test, see «TESTING»(ref-196891-S23758350142005101000000) .
  1. The cooling system has been bled according to specifications. Checking: See «COOLING SYSTEM, DRAINING AND FILLING»(ref-196862-S32357803552005100900000) (1997-99), or «COOLING SYSTEM, DRAINING AND FILLING»(ref-196866-S33984552662005100900000) (2000-03).
  2. All the air guides, covers and seals are in proper order and correctly installed.
  3. Air flow through the two dust and pollen filters is not restricted.
  4. The engine is at normal operating temperature, coolant temperature greater than 80° C (176° F).
  1. Connect VAG 1551 Scan Tool. See «VAG 1551 ((VAG 1552) SCAN TOOL (ST), CONNECTING AND SELECTING FUNCTIONS»(ref-196890-S19658011992005101000000) .
  2. Start engine and run at maximum cooling capacity for a few minutes (compressor is switched on, temperature selector at "LO" for left and right sides).
  3. Switch ignition off.
  4. Press "Rest" button (residual heating) on A/C control head - E87- A/C control head -E87- operates, coolant pump -V50- does not run, right and left heat regulating valves -N175- and - N176- closed NOTE: The time for the "Rest" function (residual heating) is limited by -E87- (to about 10 minutes).
  5. Connect VAG 1551 and select Read measuring value block, function 08 (display group 014). See «READ MEASURING VALUE BLOCK (FUNCTION 08)»(ref-196890-S05680158692005101000000) .
  6. Read off measured values of display fields 3 and 4. Specification: ambient temperature plus not more than 15 °C (59° F)
  7. Set temperature selector for left side (on -E87-) to "HI". Specified values: Temperature reading of display field 3 increases to approx. engine temperature Coolant pump -V50- running, valve -N175- open and valve -N176- closed Temperature reading of display field 4 remains approximately constant. Temperature increase less than 10° C (50° F) and valve -N176- closed.
  8. Set temperature selector for right side (at -E87-) to "HI". Specified values: Temperature reading of display field 4 increases to approx. engine temperature. Coolant pump -V50- running, valves -N175- and -N176- open
  9. Set temperature selectors for left and right sides (at -E87-) to "LO". Specified values: Temperature reading of display fields 3 and 4 drop within 5 minutes to ambient temperature, plus no more than 15° C (59° F). Coolant pump -V50- is not running, valves -N175- and - N176- are closed

A/C refrigerant system (R-134a), leak testing

  1. Use halogen leak detector Hitec HI400A-TEL or equivalent to check for refrigerant leaks.
  2. Refrigerant gas dissipates very quickly. Avoid drafty or windy areas when checking for leaks.
  3. Some refrigerant leaks are apparent by refrigerant oil deposits on or near leak location. Confirm by using leak detector.
  4. If the refrigerant system is discharged (empty), charge system with approx. 100 g (3.5 oz.) of refrigerant in order to check for leaks.

Scheme 7

Scheme 7
Scheme 7
  1. Check refrigerant system for leaks following leak detector manufacturer's instructions.
  2. Check for refrigerant leaks by passing detector probe under suspected leaking components.

Note. See leak detector manufacturer instructions.

A/C refrigerant system (R-134a), testing with pressure gauges

Due to the constant temperature/pressure relationship of R-134a, approximate high side system temperature can be determined based on system pressure.

Pressure gauges may have one or more temperature scales in addition to the pressure scale. Since various refrigerants have different temperature/pressure relationships, each gauge is specific for a particular refrigerant.

  1. Condenser and radiator clean and free of obstructions (clean if necessary)
  2. Drive belts for compressor and Generator in good condition and properly tensioned
  3. All air ducts, covers and seals OK and correctly installed
  4. Check DTC memory using VAG 1551 Scan Tool and eliminate/repair any malfunctions indicated (not affecting A/C system)
  5. All air distribution flaps reach end positions
  6. Engine at normal operating temperature
  7. Evaporator housing and heater box do not leak air (draw in secondary air) at high fresh air blower speed
  8. Outside (ambient) temperature must be between 15° - 45°C (59° - 113°F)
  9. Engine running and system set to maximum cooling ("Auto" operating mode with "LO" temperature setting selected)
  1. Switch compressor ON (the warning light in the ECON button does not light up.
  2. Temperature selection "LO" (for driver and passenger side).

If the compressor is activated (A/C clutch is switched ON)

  1. Fresh air blower -V2- runs
  2. Coolant fan -V7- runs (at least in stage 1)
  3. Closes back pressure door and opens recirculation door (within 1 minute after starting vehicle)

Note. With open recirculation door air flows out of outlets in the instrument panel even though the back pressure door is closed. If the air comes out of the instrument panel outlets, left and right heat regulating valves -N175- and -N176- of pump unit are closed and coolant pump -V50- does not run (the heater cores are not warmed up).

If one of the requirements is not met, check DTC memory and repair any malfunctions. See DIAGNOSTIC TROUBLE CODE (DTC) MEMORY, CHECKING (FUNCTION 02) .

Using VAG 1551 Scan Tool (ST), check DTC memory for any electrical, vacuum or air distribution malfunctions. See DIAGNOSTIC TROUBLE CODE (DTC) MEMORY, CHECKING (FUNCTION 02) . Correct/repair as necessary before proceeding.

  1. There are no shut off requirements for the compressor: Read measuring value block, display group 001, display field 1
  2. The triggering and function of back pressure and recirculation door is OK.
  3. All air ducts, seals and covers are OK.

If one of the following conditions exists, follow recommended service

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