Refrigerant Pressure Sensor / Switch: Testing and Inspection

High Pressure Sensor -G65- Signal, Checking







A - Refrigerant system pressure, "high pressure side" (in bar)
B - Signal ratio of square-wave signal
C - Characteristic curve

NOTE:
- Coolant Fan Control (FC) module -J293- sends a positive signal to A/C Control Head -E87- whenever the signal ratio is between 13% (equivalent to approx. 1.2 bar) and 78% (equivalent to approx. 32 bar).
- If the signal ratio is lower than 13% or higher than 78%, no positive signal is sent to -E87-. Therefore -E87- does not send a signal to -J293 instructing it to energize A/C clutch -N25.
- If the refrigerant system pressure rises above 32 bar (signal ratio higher than 78%), control unit -J293 will wait until the pressure has fallen below 24 bar (signal ratio lower than 65%) before starting to send a positive signal again.

NOTE:







- Coolant Fan Control (FC) Module -J293- switches coolant fan(s) -V7- to speed 2 whenever the refrigerant system pressure rises above 16 bar (signal ratio higher than 45%) and when Coolant Fan Control (FC) Thermoswitch -F18- is closed. If pressure falls below 12.5 bar (signal ratio lower than 37%) the control unit switches the fans back to speed 1.
- Various versions of Coolant Fan Control (FC) Module -J293-, used in conjunction with high pressure sensor -G65- may be installed. At the time of publishing however, All TT equipped with -J293- / -G65- have version where coolant fan(s) -V7- speed 1 is always switched on automatically whenever the A/C clutch -N25- is energized (regardless of refrigerant system pressure).
- Check refrigerant system pressures.
- The refrigerant pressure signal from -G65- is also input to the Motronic Engine Control Module (ECM) -J220-. This input is needed in order to react to variable A/C compressor loads dependant of refrigerant system pressure. This signal may or may not appear as a duty cycle on the read measuring value block display.

High pressure sensor -G65-, checking signal
- Connect oscilloscope test leads to -G65- signal wire electrical testing, step 4.







The oscilloscope shows this signal pattern under the following conditions:
- Ignition switched on (-G65- connected to positive and GND).
- Oscilloscope settings: 2 V/Div. = (2 volts per grid division, direct current) 5 ms/Div. (5 milliseconds per grid division).
- Oscilloscope test lead (signal wire) connected to terminal 2 on -G65-.
- Oscilloscope test lead (shielding) connected to GND.

NOTE: Signal pattern illustrated corresponds to a refrigerant system pressure of approx. 5 bar (equivalent to a signal ratio of approx. 20%). This is the pattern that occurs at an ambient temperature of 20 degrees C (68 degrees F) when the compressor is not running and the refrigerant circuit is full.







- Pulse width -A- varies according to refrigerant system pressure. When the pressure rises, the pulse width increases.
- Interval -B- between signals is always 20 milliseconds.
- The signal ratio is the ratio between pulse width -A- and signal interval -B-.