Audi Workshop Service and Repair Manuals

Checking pressure signal from high-pressure sender -G65-   Note t  On vehicles with automatically controlled air conditioner, the operating and display unit, Climatronic control unit -J255- evaluates the signal from the high-pressure sender -G65- and actuates the air conditioner compressor by way of the air conditioner compressor regulating valve -N280-. t  On vehicles with manually controlled air conditioner, the air conditioning system control unit -J301- evaluates the signal from the high-pressure sender -G65- and actuates the air conditioner compressor by way of the air conditioner compressor regulating valve -N280-. t  The cooling output cannot be checked with the high-pressure sender -G65- removed; the operating and display unit, Climatronic control unit -J255- / air conditioning system control unit -J301- does not switch on the air conditioner compressor → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051. t  Depending on the version of the high-pressure sender -G65-, the measured value for the pressure in the refrigerant circuit transmitted by the high-pressure sender -G65- may be too low at low ambient temperatures (ambient temperature less than 5 °C) although the air conditioner is OK and the refrigerant circuit has been properly charged. A fault entry may therefore be erroneously made at low ambient temperatures (ambient temperature less than 5 °C) in the air conditioning system control unit -J301- or with air conditioner operating and display units, Climatronic control unit -J255- with part number „8P0 820 043“ up to index „AH“ (fault memory entry: High-pressure sender -G65-„Lower limit value not reached“). If the fault is only displayed as a sporadic fault at ambient temperatures calculated by the air conditioner of above 5 °C and the air conditioner is functioning properly, the fault memory entry can be erased (no further action is necessary). t  The fitting locations differ depending on the engine. On vehicles with 2.0 l diesel engine, the high-pressure sender -G65- for example is not fitted at the refrigerant line from the expansion valve to the condenser, but rather at the refrigerant line between the air conditioner compressor and the condenser. t  On vehicles with 4-cyl. engine, the connector of the high-pressure sender -G65- can currently be unplugged without having to remove other components (accessible from above). t  After switching off the air conditioner compressor, a relatively long period may elapse with this vehicle before the pressure on the high-pressure end decreases (the expansion valve is cold and the pressure on the low-pressure end increases rapidly after switch-off, the expansion valve closes and the refrigerant can only flow slowly to the low-pressure end). –  Remove the noise insulation (e.g. on vehicles with 6-cyl. engine). → General body repairs, exterior ; Rep. gr.66

–  Unplug the connector -A-.

Pin assignment at high-pressure sender -G65- Contact -1- Earth Contact -2- Signal output (square-wave signal to operating and display unit, Climatronic control unit -J255- / air conditioning system control unit -J301-) Contact -3- Positive (terminal „75“)   Note t  The air conditioner compressor is not switched on if the connector -A- is unplugged. t  The high-pressure sender -G65--B- is an electronic control unit which generates a square-wave signal with a ratio which varies with the pressure in the refrigerant circuit. Pressure signal from high-pressure sender -G65-

-A- Pressure on high-pressure end of refrigerant circuit in bar (absolute) -B- Ratio of square-wave signal. -C- Characteristic curve for ratio of square-wave signal.   Note t  As soon as there is no compressor shut-off criterion, the operating and display unit, Climatronic control unit -J255- / the air conditioning system control unit -J301- switches on the air conditioner compressor (by actuating the air conditioner compressor regulating valve -N280-) → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051. t  Depending on the version of the high-pressure sender -G65-, the measured value for the pressure in the refrigerant circuit transmitted by the high-pressure sender -G65- may be too low at low ambient temperatures (ambient temperature less than 5 °C) although the air conditioner is OK and the refrigerant circuit has been properly charged. A fault entry may therefore be erroneously made at low ambient temperatures (ambient temperature less than 5 °C) in the air conditioning system control unit -J301- or with air conditioner operating and display units, Climatronic control unit -J255- with part number „8P0 820 043“ up to index „AH“ (fault memory entry: High-pressure sender -G65-„Lower limit value not reached“). If the fault is only displayed as a sporadic fault at ambient temperatures calculated by the air conditioner of above 5 °C and the air conditioner is functioning properly, the fault memory entry can be erased (no further action is necessary). t  If the ratio is greater than 12 % (corresponding to approx. 1.2 bar absolute) and less than 78 % (corresponding to approx. 32 bar absolute) t  If the signal ratio is less than 12 % or greater than 78 %, the air conditioner compressor is not switched on (the air conditioner compressor regulating valve -N280- is not actuated). t  The signal ratio and the pressure calculated by the operating and display unit, Climatronic control unit -J255- / air conditioning system control unit -J301- are indicated in the measured value block → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051. t  At absolute pressure, 0 bar corresponds to an absolute vacuum. Normal ambient pressure thus corresponds to roughly 1 bar absolute. On the scales of most pressure gauges, 0 bar corresponds to an absolute pressure of approx. 1 bar (can be seen from „-1“ mark below „0“).

t  Depending on the pressure calculated in the refrigerant circuit, the operating and display unit, Climatronic control unit -J255- / the air conditioning system control unit -J301- transmits the request for increased radiator fan -V7- speed to the engine control unit via the data bus with the air conditioner compressor actuated (at a certain pressure in the refrigerant circuit or as soon as the air conditioner compressor is switched on irrespective of the pressure, depending on the version). The request determined by the operating and display unit, Climatronic control unit -J255- / air conditionng system control unit -J301- is indicated in the measured value block → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051 (reading measured value block). t  At present the radiator fan request is transmitted at the following signal ratio: t  Pressure in refrigerant circuit less than approx. 9 bar (6 bar if pressure previously greater than 9 bar): No request t  Pressure in refrigerant circuit greater than approx. 9 bar (6 bar) up to approx. 20 bar: 30 to 100 % request depending on pressure t  If the pressure in the refrigerant circuit is greater than approx. 20 bar, the resultant request is roughly 100 %. t  The signal generated by the high-pressure sender -G65- is also used for engine control. The operating and display unit, Climatronic control unit -J255- / air conditioning system control unit -J301- transmits the information by way of the convenience data bus system to the engine control unit (the torque required to drive the air conditioner compressor is governed by the pressure in the refrigerant circuit). Depending on the version of the engine control unit, the signal is displayed as a ratio in the measured value block → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051 (for the engine control unit fitted).

This pattern will appear on the oscilloscope screen (e.g. on the vehicle diagnostic, testing and information system -VAS 5051 A-) if the following conditions are satisfied. –  Ignition on (positive at contact „3“ and earth at contact „1“ at high-pressure sender -G65-) –  Setting on oscilloscope: 5 V/div. DC (5 V per unit DC voltage) 5 ms/div. (5 milliseconds per unit) –  Test lead (signal wire) connected to contact „2“ at high-pressure sender -G65-. –  Test lead (screen) connected to contact „1“ (earth at high-pressure sender -G65-).   Note t  The illustration shows the signal transmitted at a refrigerant circuit pressure of approx. 7 bar absolute, corresponding to a signal ratio of approx. 25 % (level occurring with air conditioner compressor not running, ambient temperature of 30 °C and refrigerant circuit charged). t  The pulse width -A- is governed by the pressure in the refrigerant circuit (area -A- becomes broader as pressure increases). t  The signal distance -B- is always 20 milliseconds (corresponding to a frequency of 50 hertz). t  The signal ratio is derived from the ratio of pulse width -A- to signal distance -B-.

t  Test leads from the adapter set -V.A.G 1594/C- can be employed for example for this test or an adapter lead can be made. For this, use one connector -A- and -B- each (with part number 1J0 973 703 and 1J0 973 803 and the corresponding plug contacts → Electronic parts catalogue), two commercially available sockets for banana plugs -C- and three wires with a cross section of 0.5 mm2 for example.