Air Conditioning: Diagnosis Audi A6 C5 facelift

A/C system cooling performance, testing

Note. Under certain operating conditions, residual moisture in refrigerant circuit can lead to an ice build-up at compressor regulator valve. Compressor control is reduced by this ice build-up, evaporator is cooled too intensely and freezes. The freeze-up of the evaporator can be the cause for the following customer complaints: After a long drive, A/C system repeatedly or sporadically fails (no cooling or heating performance), after switching off vehicle and after a short time, A/C function is OK again. After a long drive, windows fog up from inside, windows are also not cleared by pressing the "Defrost" button, after switching off vehicle and after a short time, A/C function is OK again. Corrective action: For vehicles as of model year 2002 and a compressor with A/C Compressor Regulator Valve -N280-, check measured value of Evaporator Vent Temperature Sensor -G263-. See DISPLAY GROUP 010: MEASURING VALUES FOR EVAPORATOR VENT TEMPERATURE SENSOR -G263-, FRESH AIR INTAKE DUCT TEMPERATURE SENSOR -G89-, OUTSIDE AIR TEMPERATURE SENSOR -G17- AND CALCULATED OUTSIDE TEMPERATURE TRANSMITTED TO INSTRUMENT CLUSTER . If measured value of the sensor is too low under operating conditions specified by customer (at an ambient temperature above 0 6 C, colder than 0 C for a long period of time although A/C Compressor Regulator Valve -N280- is not currently being activated), transfer vehicle to an authorized service shop for A/C systems. In vehicles without Evaporator Vent Temperature Sensor -G263- e.g. via Sender for outlet temperature, floor outlet -G192-, check at the adjustment: "Temperature Lo" for driver's- and passenger side, 4 or 5 bars for fresh air blower RPM, air outlet in footwell and fresh air operation under operating conditions specified by customer. If measured value of the sensor is too low (at an ambient temperature above 0 ° C, colder than 0 ° C for a long period of time), transfer vehicle to an authorized service shop for A/C systems. Check refrigerant line from evaporator to accumulator (thick tube, low pressure side) with engine running. If this line is thickly iced-up when complaint occurs (a very thin layer of ice is permitted), this indicates that the temperature in evaporator is too low, transfer vehicle to an authorized service shop for A/C systems. Bring the determined deficiency to the attention of the authorized service shop for A/C systems, the necessary work can only be performed there (draining refrigerant circuit, replacing accumulator and then evacuating the refrigerant circuit for a minimum of 3 hours).

Test requirements

1. Radiator and condenser clean (clean if necessary)
2. Ribbed belt OK and correctly tensioned and drive plate actually drives compressor (6 and 8 cylinder gas engine).
3. Compressor drive unit (connection between compressor and engine) is correctly installed (only Audi Allroad with 4.2 L engine, see «COMPRESSOR DRIVE UNIT, CHECKING, REPLACING»(ref-196290-S08476983422005100800000) ).
4. Air flow through dust and pollen filter not obstructed by dirt
5. Air conditioner unit properly sealed (when fresh air blower is at maximum speed setting, no additional air is drawn in; air delivery is via vents only)
6. Vehicle not standing in direct sunlight Engine at normal operating temperature All instrument panel vents open.
7. Engine running and A/C control head -E87- set as follows: AUTO mode Compressor switched on (LED in ECON button not lit up) Temperature selection LO (for both driver's and passenger's side) Compressor activated (A/C clutch -N25- switched on) A/C Compressor Regulator Valve -N280- is switched on (on vehicles using -N280-. See «MEASURING VALUE BLOCKS (VEHICLES FROM MODEL YEAR 2002)»(ref-196289-S29586168492005100800000) (display group 001 and 002). Coolant Fan -V7- running (speed depends on pressure in refrigerant circuit and engine temperature) Fresh Air Blower -V2- running at maximum speed Fresh air/recirculated air flap moved to "recirculated air" mode (within 1 minute of starting engine) Air should come out of the instrument panel vents Both temperature flaps in "cooling" position

Note. Check DTC memory if one test requirement is not attained. See CHECK DTC MEMORY (FUNCTION 02) . And carry out output Diagnostic Test Mode. See OUTPUT DIAGNOSTIC TEST MODE (DTM) .

A/C refrigerant system, 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 1

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. Refer to leak detector manufacturer's instructions.

A/C refrigerant system, 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.

Using VAG 1551 Scan Tool (ST), check DTC memory for any electrical, vacuum or air distribution malfunctions. Correct/repair as necessary berfore proceeding. See ON BOARD DIAGNOSTIC (OBD), INITIATING .

1. There are no shut off requirements for the compressor; read measuring value block, display group 001, display field 1
2. Triggering and function of air flow flap and fresh air/recirculated air flap OK
3. All air ducts, seals and covers are OK

If one of the following conditions exists, follow recommended service