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Auxiliary Fan Switch Replacement
 
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Pelican Technical Article:

Auxiliary Fan Switch Replacement

Steve Vernon

Time:

30 minutes30 mins

Tab:

$10 to $50

Talent:

**

Tools:

22mm wrench, bucket, rags

Applicable Models:

Mercedes-Benz W123 (1977-85)

Parts Required:

Auxiliary fan switch

Hot Tip:

If you are really quick you don't need to drain the coolant

Performance Gain:

Working fan

Complementary Modification:

Coolant flush

The auxiliary fan switch takes a reading of the coolant temperature and uses this signal to turn the fan on. This can happen when stuck in traffic or if the coolant just reaches a temperature that requires extra air flow through the radiator.

The switch is easy to replace if it fails and if you are fast enough you can do it without draining the coolant from the vehicle. Just remember to check the level after you have installed the new one and top up the coolant as needed.

Whether you are draining the coolant to a level below the switch or just changing it fast, make sure that you are working on a cool car. Please see our article on radiator flush and fill if you want to drain the coolant.

Remember your car may have been serviced before and parts replaced with different size fasteners used in the replacement. The sizes of the nuts and bolts we give may be different from what you have so be prepared with different size sockets and wrenches.

Protect your eyes, hands and body from fluids, dust and debris while working on your vehicle. If working with the electrical system, disconnect the battery before beginning. Recycle parts, packaging and fluids when possible. Never work on your vehicle if you feel the task is beyond your ability.

Our vehicle may vary slightly from yours as models do change and evolve as they grow older. If something seems different, let us know and share your info to help other users. Questions or want to add to the article? Leave a comment below. When leaving a comment, please leave your vehicle information.

The auxiliary fan switch is located below the upper radiator to thermostat housing hose (red arrow).
Figure 1

The auxiliary fan switch is located below the upper radiator to thermostat housing hose (red arrow). I removed the hose for photographic purposes, if you want to remove the hose to give you more room you must drain the coolant below the thermostat housing level.

The switch is located on the back left side of the thermostat housing (red arrow).
Figure 2

The switch is located on the back left side of the thermostat housing (red arrow). You can move the hose out from the bracket in front of the switch to give you more room.

Remove the electrical connection on the end of the switch (red arrow).
Figure 3

Remove the electrical connection on the end of the switch (red arrow).

If you are not draining the coolant you will want to remove the old switch and install the new one as quick as you can.
Figure 4

If you are not draining the coolant you will want to remove the old switch and install the new one as quick as you can. Even working quickly some coolant will escape so be prepared to catch it and dispose of it correctly. Place a 22mm wrench on the switch and remove it (red arrow).

Remove the old switch and install the new one.
Figure 5

Remove the old switch and install the new one. Coolant will escape through the opening (red arrow) if you have not drained the system so remember to check the level when you are done and top it up accordingly.

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Page last updated: Fri 12/9/2016 02:59:20 AM