Sensors and Valve Connections

NOTE:
- As a running change in production, pressure switch - F129 is replaced by high pressure sensor - G65 -.
- The function of Coolant Fan Control (FC) Module - J293 and vehicle wiring layout will vary depending on whether vehicle is equipped with A/C pressure switch - F129 - or high pressure sensor - G65 -.


A/C pressure switch - F129 -







A/C clutch - N25 - is disengaged when - F129 - detects insufficient or excessive refrigerant system pressures (A/C compressor protection).
The coolant fan(s) - V7 - are also switched to speed 2 when - F129 - detects an increase in refrigerant system pressure.
Switching pressures. Refer to "A/C Refrigerant System, Servicing" Service and Repair
Removing and installing. Refer to "A/C Refrigerant System, Servicing" Service and Repair

High pressure sensor - G65 -







High pressure sensor - G65 - B -, transmits a square wave signal (to Coolant Fan Control (FC) Module - J293 - ) at a rate which varies according to the refrigerant system pressure.

- J293 reacts to the pulse rate of the signal from - G65 as follows: 1) It informs the A/C control head - E87 - that the pressure in the refrigerant system is OK and that A/C clutch - N25 - can be switched on (compressor is switched on via - J293 - ). 2) If the refrigerant system pressure rises, the control unit switches the radiator fan(s) to speed 2.

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 - I - G65 - combination have version where coolant fan(s) - V7 - speed I is always switched on automatically whenever the A/C clutch - N25 - is energized (regardless of refrigerant system pressure).

The signal generated by high pressure sensor - G65 - is also provided as an input to the Motronic Engine Control Module (ECM). As the amount of torque needed to drive the A/C compressor varies according to the refrigerant system pressure, the ECM processes this signal in order to enhance engine performance. Depending on the type of ECM, this signal may or may not appear as a duty cycle on the read measuring value block display (function 08).

Checking signal. Refer to Coolant Fan Control (FC) Module - J293 - (Vehicles With High Pressure Sensor - G65 - ), Electrical Testing under Cooling System/Cooling Fan Control Module Testing and Inspection

Valve connections for pressure switch/sensor







The A/C system pressure switch/sensor use a different size thread than the service connection.
Use only the proper O-rings for pressure switch/sensor connections.

A - Connection (lubricated)
B - O - ring seal
C - Valve