Checking signal from high-pressure sender -G65 — AUDI

A - Pressure on high-pressure side of refrigerant circuit in bar

B - Signal ratio of the square-wave signal

C - Curve

Notes:

Control unit -J293 transmits a positive signal to operating and display unit -E87:
When duty cycle is larger than 13% (equivalent to approx. 1.2 bar) and less than 78% (equivalent to approx. 32 bar).
If the duty cycle is less than 13% or greater than 78%, no positive signal is transmitted to -E87, and -E87 transmits no signal to -J293 - as a result -J293 does not switch on the compressor (via magnetic clutch -N25).

If the refrigerant circuit pressure was greater than 32 bar (duty cycle greater than 78%), control unit -J293 does not re-transmits a positive signal to -E87 until the pressure drops below 24 bar (duty cycle less than 65%).

Control unit -J293 switches radiator fan -V7 to speed 2:
As soon as the refrigerant circuit pressure exceeds 16 bar (duty cycle exceeds 45%). If the pressure drops below 12.5 bar (duty cycle drops below 37%), the fans are switched back to 1st speed.
Coolant thermoswitch -F18 closed.

The control unit -J293, installed in vehicles with high-pressure sender -G65, is available in several designs. Only the design in which the radiator fan is always switched on with the compressor is currently installed in the Audi TT (the first fan speed is switched on independently from the pressure in the refrigerant circuit).
The signal generated by high-pressure sender -G65 is also used for engine control (the required compressor drive torque is governed by the refrigerant circuit pressure). Depending on the engine control unit version, the signal in the measured value block is displayed as duty cycle.

=> Relevant Workshop Manual, Injection and Ignition system

Check signal from -G65

Connect test lead of one oscilloscope to the signal wire of high-pressure sender -G65 (=> Page
01-155
test step 4).

This display appears on the oscilloscope screen if the following conditions have been satisfied.

Ignition switched on (positive and earth applied at sender -G65)
Oscilloscope setting:
2 V/Div. = (2 V DC per unit)
5 ms/Div. (5 milliseconds per unit)
Test lead (signal wire) at contact 2 of high-pressure sender -G65.
Test lead (screening) connected to earth.

Notes:

The illustration shows the signal transmitted at a refrigerant circuit pressure of approx. 5 bar overpressure, which is equivalent to a duty cycle of approx. 20% (automatic adjustment with compressor at a standstill, at an ambient temperature of 20 °C, and with filled refrigerant circuit).

Pulse width -A- is governed by the refrigerant circuit pressure (if the pressure increases, the -A- range widens).
Signal gap -B- is always 20 milliseconds.
The signal ratio is derived from the ratio between pulse width -A- and signal gap -B-.