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    2000 Mazda MX-5 Miata 1.8L MFI DOHC 4cyl

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    VW Passat & Audi A4 1990-2000

    Engine Cooling Fan Thermal Switch

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    The engine's electric fan switch is mounted into the cooling passage of the radiator or into one of the lower coolant pipes coming from the bottom of the radiator. The fan switch is a temperature sensitive two stage thermal switch that remains open (OFF) until the coolant reaches a certain temperature.

    The 2-stage thermal switch essentially is 2 thermal switches that have been combined into one thermal switch. The stage 1 or low speed circuit is closed (ON) when the coolant temperature reaches approximately 203°F (95°C). The stage 2 or high speed circuit is closed (ON) when the coolant temperature reaches approximately 221°F (105°C).

    The thermal switch has three terminals and is used to complete a series circuit. On 1990-93 Passat models, the thermal is fed positive battery current and the switch, when closed (ON), completes the circuit for the positive battery voltage for the cooling fan(s).

    The thermal switch used on A4 and 1994 and later Passat models is used to complete a series circuit that supplies ground to trigger a relay, which is used to complete the positive battery voltage for the cooling fan(s).



    Click image to see an enlarged view

    Fig. The cooling fan thermal switch is located on the bottom corner of the radiator on 1.8L Passat models

    TESTING

    The electric cooling fan switch is installed into a coolant passage and operates the radiator auxiliary electric cooling fan when the coolant temperature reaches a specified temperature or when the air conditioner is activated. The fan has operates in two stages depending on the engine coolant temperature.


    NOTE
    In normal conditions, if the air conditioner is in proper working order, the engine cooling fans will operate when the air conditioner is turned on, because the A/C operation overrides the thermal switch, regardless of the coolant temperature. When testing the electric cooling fan circuit, make sure the air conditioner is OFF.

    Electric Cooling Fan Operation

    Operation of the cooling fan is dependent on several factors, which include proper thermostat operation, A/C operation, and other switches, including the after-run thermoswitch. Before testing the thermal electric fan switch, quickly verify the operation of the electric cooling fan(s). Make sure that the cooling system is functioning properly, as problems such as a restricted radiator will cause overheating problems and may exhibit the same symptoms as a cooling fan malfunction. Make sure all the fuses, electrical connections, and wires are intact.

    1990-93 Passat models:

    CAUTION
    Keep clear of the radiator fan blades. The fan can operate at any time.

    1. Unplug the electrical harness connector from the thermal fan switch.
    2.  
    3. Turn the ignition switch to the ON position, but Do NOT start the engine.
    4.  
    5. Check for battery voltage at terminal No. 3 (red wire). If battery voltage is not present, check the fuse and wiring and repair as necessary. The cooling fan operation can still be verified if a fused jumper wire is used to supply positive battery voltage. If doing so, connect the jumper wire used for probing the electrical connector to the alternate source of positive battery voltage and substitute the alternate positive battery voltage instead of terminal No. 3 (red wire) and proceed with testing.
    6.  
    7. Using a suitable jumper wire, carefully connect the jumper between terminal Nos. 2 (red wire with white tracer) and 3 (red wire). The radiator cooling fan should operate at low speed.
    8.  
    9. Using a suitable jumper wire, connect the jumper between terminal 1 (red wire with black tracer) and 3 (red wire). The radiator fan should operate at high speed.
    10.  
    11. If the radiator fan operates properly at both speeds, and battery voltage is available at terminal 3 (red wire), the radiator fan switch is faulty and should be replaced.
    12.  
    13. If the radiator fan does not operate, check the radiator fan or the wiring circuit for broken terminals, blown fuses, cut wires, etc. For additional information, please refer to the following topic(s): Chassis Electrical, Wiring Diagrams.
    14.  

    A4 and 1994-00 Passat models

    CAUTION
    Keep clear of the radiator fan blades. The fan can operate at any time.

    1. Unplug the electrical harness connector from the thermal fan switch.
    2.  
    3. Check for ground at terminal 3 (brown wire). If ground is not present, check the wiring and repair as necessary. The cooling fan operation can still be verified if a suitable jumper wire is used to supply ground. If doing so, connect the jumper wire used for probing the electrical connector to the alternate source of ground and substitute the alternate ground instead of terminal 3 (brown wire) and proceed with testing.
    4.  
    5. Turn the ignition switch to the ON position, but Do NOT start the engine.
    6.  
    7. Using a suitable jumper wire, carefully connect the jumper between terminals 2 (green wire with black tracer) and 3 (brown wire). The radiator cooling fan should operate at low speed.
    8.  
    9. Using a suitable jumper wire, connect the jumper between terminals 1 (red wire with green tracer) and 3 (brown wire). The radiator fan should operate at high speed.
    10.  
    11. If the radiator fan operates properly at both speeds, and ground is available at terminal 3 (brown wire), the radiator fan switch is faulty and should be replaced.
    12.  
    13. If the radiator fan does not operate, check the relays, radiator fan or the wiring circuit for broken terminals, blown fuses, cut wires, etc. For additional information, please refer to the following topic(s): Chassis Electrical, Wiring Diagrams.
    14.  

    Cooling Fan Thermal Switch
    Switch Installed

    CAUTION
    Do NOT allow the engine to operate continuously without the aid of the auxiliary cooling fan otherwise severe engine damage will occur.

    1. Locate the cooling fan switch mounted on the radiator.
    2.  
    3. Detach the wire connector from the fan switch.
    4.  
    5. To test stage 1 of the fan switch, using a suitable ohmmeter or continuity tester check for continuity between the fan switch terminals 2 and 3 .
    6.  
    7. Allow the engine to reach a coolant temperature as follows. The fan switch should have continuity (switch closed) at this temperature:
    8.  

    1990-93 Passat models:



    Stage 1: 203°F (95°C)
     

    A4 and 1994-00 Passat models:



    Stage 1: 198-207°F (92-97°C)
     

    1. To test stage 2 of the fan switch, using a suitable ohmmeter or continuity tester check for continuity between the fan switch terminals 1 and 3 .
    2.  
    3. Allow the engine to reach a coolant temperature as follows. The fan switch should have continuity (switch closed) at this temperature:
    4.  

    1990-93 Passat models:



    Stage 2: 221°F (105°C)
     

    A4 and 1994-00 Passat models:



    Stage 2 : 210-221°F (99-105°C)
     

    1. The thermal switch should be open (off) as follows:
    2.  
    3. Stage 1: 183-196°F (84-91°C)
    4.  
    5. Stage 2 : 196-208°F (91-98°C)
    6.  
    7. If the switch does not operate within the range of the supplied information, replace the switch.
    8.  

    Switch Removed

    WARNING
    Submerging the electric cooling fan switch below the threads could damage the component. Perform this procedure in a safe and well-ventilated area. Wear eye protection and use care to not come in contact with any of the heated components. Do NOT use a heating device that produces an open flame.

    Testing a radiator fan switch is not difficult, however to do so requires some basic equipment. To properly test the fan switch, the switch's probe must be submersed in heated coolant, only as far as the component's threads. The coolant must be heated while the temperature is monitored. When the coolant reaches the specified temperature, the fan switch should be closed. Use suitable fitting electrical jumper leads to avoid contact with the heated coolant during testing. Testing the switch requires the following equipment:



    A safe source of heat, such as a portable electric hot plate
     
    A container capable of being safely heated by a hot plate and handling heated coolant
     
    A thermometer safely capable of reading 221°F (105°C)
     
    A device to safely hold the switch such that only the coolant probe is submerged into the coolant
     
    An ohmmeter or continuity tester
     

    1. Refer to the cooling fan switch removal and installation warning and procedures and remove the switch.
    2.  
    3. Attach a 12 inch wiring sub-harness to the cooling fan switch to avoid having to probe the switch while in the heated coolant. Place the switch into a suitable holding device such that the temperature probe of the switch is submersed in a container of heated coolant. Make sure the container can be safely heated using a suitable source of heat such as a portable electric hot plate.
    4.  
    5. Using a suitable thermometer to measure the coolant temperature, heat the coolant until the specified temperature is attained.
    6.  
    7. To test stage 1 of the fan switch, using a suitable ohmmeter or continuity tester check for continuity between the fan switch terminals 2 and 3 . The cooling fan switch should have continuity (closed) between the electrical terminals 2 and 3 at the following temperatures:
    8.  

    1990-93 Passat models:



    Stage 1: 203°F (95°C)
     

    A4 and 1994-00 Passat models:



    Stage 1: 198-207°F (92-97°C)
     

    1. To test stage 2 of the fan switch, using a suitable ohmmeter or continuity tester check for continuity between the fan switch terminals 1 and 3 . The cooling fan switch should have continuity (closed) between the electrical terminals 1 and 3 at the following temperatures:
    2.  

    1990-93 Passat models:



    Stage 2: 221°F (105°C)
     

    A4 and 1994-00 Passat models:



    Stage2 : 210-221°F (99-105°C)
     

    1. The thermal switch should be open (off) as follows:
    2.  
    3. Stage 1: 183-196°F (84-91°C)
    4.  
    5. Stage 2 : 196-208°F (91-98°C)
    6.  
    7. If the switch does not operate within the range of the supplied information, replace the switch.
    8.  

    REMOVAL & INSTALLATION

    CAUTION
    Engine coolant can spray out causing severe burns if the Engine Coolant Temperature (ECT) gauge sending unit is removed from a hot engine without allowing the engine to cool below 100°F (37°C) and draining the engine coolant into a sealable container first.

    1. Allow the engine to cool below 100°F (37°C) before working on the cooling system.
    2.  
    3. Note the anti-theft code and radio presets for the radio.
    4.  
    5. Disconnect the negative battery cable.
    6.  
    7. Raise and safely support the front of the vehicle on jackstands.
    8.  
    9. If necessary, remove the lower engine shield.
    10.  
    11. Locate the cooling fan thermal switch.
    12.  
    13. Drain the engine coolant into a sealable container.
    14.  
    15. Detach the electrical connector.
    16.  
    17. If the thermal switch is held into the coolant passage with a retaining clip:
    18.  
      1. Remove the thermal switch retaining clip, and pull the thermal switch straight out of the housing.
      2.  

    19. If the thermal switch is threaded into the coolant passage:
    20.  
      1. Loosen the thermal switch using a crowfoot wrench, a suitable boxed end wrench or a thin-walled 3 / 8 inch drive 12-point, deep-well socket and breaker bar.
      2.  


    To install:

    1. If the thermal switch is held into the coolant passage with a retaining clip:
    2.  
      1. Install a new O-ring on the sensor.
      2.  
      3. Using a small amount of fresh coolant or an anti-seizing compound, lightly lubricate the O-ring, and push the thermal switch in the housing.
      4.  
      5. While pushing inward on the thermal switch, install the retaining clip.
      6.  

    3. If the thermal switch threaded into the coolant passage:
    4.  
      1. Install the sensor with a new crush washer and tighten to 26 ft. lbs. (35 Nm).
      2.  

    5. Plug in the harness connector to the thermal switch.
    6.  
    7. As applicable, install the lower splash shield.
    8.  
    9. Lower the vehicle from the jackstands.
    10.  
    11. Refill the cooling system with the proper type and mixture of coolant and bleed as necessary. For additional information, please refer to the following topic(s): General Information and Maintenance, Fluids and Lubricants.
    12.  
    13. Reconnect the negative battery cable and re-code the radio as necessary.
    14.  
    15. Start the engine, check for normal operation and fluid leaks.
    16.  

     
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