Radiator Cooling Fan: Description and Operation

(Alldata Editor's Note: VW does not provide easy access to Description and Operation information for the cooling fans V7 and V35. Below is a brief explanation of the various inputs from the cooling and air conditioning systems which effect cooling fan operation. Always refer to the appropriate wiring diagrams when diagnosing cooling fan faults.)

Coolant Fan Control

The Coolant Fans (V7/V35) are primarily controlled by the following:
- Coolant Fan Control (FC) Thermal Switch F18
- For V7, Third Speed Coolant Fan Control (FC) Thermal Switch F165 / Third Speed Coolant Fan Control (FC) Relay J135
- Coolant Fan Control (FC) Control Module J293
- A/C Pressure Switch F129 (via J293), if equipped
- High Pressure Sensor G65 (via J293), if equipped

When A/C is off:
- F18 switches the fans on to first speed when coolant temperature is within first stage switching temperature range.
- F18 switches the fans on to second speed (via J293) when coolant temperature is within second stage switching temperature range.

When A/C is on:
- J293 switches the fans on to first speed.
- If equipped, A/C Pressure Switch F129 switches the fan(s) to the second speed (via J293) when refrigerant circuit pressure increases.
- If equipped with High Pressure Sensor G65, J293 switches the fan(s) to the second speed if the refrigerant system pressure rises.

In addition, F165 switches on coolant fan to third speed via J135 relay when coolant temperature is within third stage switching temperature range.

Coolant Fan Control (FC) Thermal Switch F18
Switching temperatures:
1st stage
On: 92 - 97 �C
Off: 84 - 91 �C
2nd stage
On: 99 - 105 �C
Off: 91 - 98 �C

Third Speed Coolant Fan Control (FC) Thermal Switch F165
Switching temperatures:
On: 112�C / 234�F
Off: 108�C / 226�F

Coolant FC (Fan Control) Control Module J293





Note: Available in different construction styles, some separate some installed on radiator fan.


This control module switches on and off the A/C clutch and therefore the A/C compressor. It switches the coolant fan and calculates the pressure in the refrigerant circuit on vehicles with High Pressure Sensor G65 or A/C Pressure/temperature Sensor G395.

A/C Pressure Switch F129






F129 has three functions:
- Switches the A/C clutch N25 off (via J293) when excessive refrigerant circuit pressure is present (e.g.: insufficient air flow over condenser or when overcharged).
- Switches the A/C clutch N25 off (via J293) when insufficient refrigerant circuit pressure is present (e.g.: when refrigerant has leaked out)
- Switches on the second speed coolant fan V7 when refrigerant circuit pressure increases (approx. 16 bar).

Note:
- The presence of F129 is engine dependant. Where F129 is not used, high pressure sensor G65 is used instead.
- Always confirm system use of either F129 or G65 and applicable wiring circuit using applicable "Engine" and "Air conditioning" wiring diagrams.
- A/C Pressure Switch F129 replaces the A/C Refrigerant High Pressure Switch F23, A/C Refrigerant Low Pressure Switch F73 and the A/C Refrigerant High Pressure Switch F118.

High Pressure Sensor G65






Where equipped, the High Pressure Sensor G65 transmits a square wave signal to Coolant Fan Control (FC) Module J293 at a rate which varies according to the refrigerant system pressure.

The signal from High Pressure Sensor G65 is processed as follows:

Based on the pulse rate transmitted by the High Pressure Sensor G65, the Coolant Fan Control (FC) Module J293 determines the A/C refrigerant system pressure and controls the function of the A/C Clutch N25 and Coolant Fans accordingly. For example:

- Switches the Coolant Fan V7 to the next higher speed when pressure in the refrigerant circuit increases.
- Switches off A/C Clutch N25 when pressure is excessive (for example when engine cooling is insufficient).
- Switches off A/C Clutch N25 off when pressure is too low (for example with low/no refrigerant).

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.

Note:
- The presence of G65 is engine dependant. Where G65 is not used, A/C pressure switch F129 is used instead.
- Where G65 is used, its wiring circuit varies according to engine application (E.g.: some are connected to the ECM, some are not).
- Always confirm system use of G65 and applicable wiring circuit using applicable "Engine" and "Air conditioning" wiring diagrams.