SEAT Workshop Service and Repair Manuals

Checking pressure signal from high-pressure sender -G65-   Note The function of the high pressure sender -G65- can be checked using the self diagnostics of the Climatronic control unit -J255- / the Air conditioning control unit -J301- → Vehicle diagnostic tester.

–  Unplug 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 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 in high-pressure side of refrigerant circuit in bar (absolute) -B- Duty cycle of square-wave signal -C- Characteristic curve for duty cycle 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  If the duty cycle is over 12 % (equivalent to approx. 1.2 bar absolute pressure) and below 78 % (equivalent to approx. 32 bar absolute pressure). 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 duty cycle and the pressure calculated by the operating and display unit (Climatronic control unit -J255-) / air conditioning system control unit -J301- is displayed in the measured value block → Guided Fault Finding function of vehicle diagnostic, testing and information system VAS 5051. t  An absolute pressure of 0 bar represents an absolute vacuum. Normal ambient pressure thus corresponds to an absolute pressure of roughly 1 bar. On the scales of most pressure gauges, 0 bar corresponds to an absolute pressure of 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 conditioning system control unit -J301- is indicated in the measured value block → Guided Fault Finding function of vehicle diagnostic, testing and information system VAS 5051. t  The request for radiator fan is currently transmitted with the following duty cycle: t  Pressure in the refrigerant circuit lower than approx. 9 bar (6 bar when the pressure was more than 9 bar) without requirement. t  Pressure in the refrigerant circuit higher that approx. 9 bar (6 bar) to approx. 20 bar, depending on the pressure of 30 to 100 % of the requirement. t  If the pressure in the refrigerant circuit is higher than approx. 20 bar, a requirement of about 100 % results. 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 a duty cycle in the measured value block → Guided Fault Finding function of vehicle diagnostic, testing and information system VAS 5051 (for the respective engine control unit installed.)

This pattern will appear on the screen of an oscilloscope (e.g. vehicle diagnostic, testing and information system -VAS 505X-) if the following conditions are met: –  Ignition on (positive at contact „3“ and earth at contact „1“ of high-pressure sender -G65-) –  Oscilloscope adjustment: 5 V/Div. = (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 corresponds to a duty cycle of approx. 25 %. (level occurring with air conditioner compressor not running, ambient temperature of 30 °C and refrigerant circuit charged). t  Pulse width -A- is governed by pressure in 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 duty cycle is derived from the ratio of pulse width -A- to signal distance -B-.

t  For this test you can use e.g. test leads from the auxiliary measuring set -V.A.G 1594/C- or an improvised adapter lead. 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.