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landy andy



Member Since: 15 Feb 2009
Location: Ware, Herts
Posts: 5820
2006 Defender 110 Td5 USW Zermatt Silver
AC fan running when not requested
Got an issue where my AC fan is running when my AC isn’t being used (don’t really use the AC).

I know the fan can be used to cool the engine if the ECU thinks the engine is too hot, so gets the AC fan to help, but mine is coming on as soon as I start the engine, even when minus temps. Most of the time I can then briefly run the AC, then when I turn off the AC the fan also turns off, and I think that is it till next time.

Drove a couple of hours Friday and when I got to destination AC fan running. My engine temps never even get to mid position, and all cooling system runs well. Today on way back stopped at fuel station after an hour, and fan running. This time operating the AC, then AC off, doesn’t stop the fan running. Pulling the relay did though.

Any thoughts?
Post #1061148 23rd Feb 2025 3:26pm
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MadTom



Member Since: 10 Sep 2013
Location: Olomouc
Posts: 642
Czech Republic 1999 Defender 130 Td5 HCPU Baltic Blue
Take a diagnostics equipment and look for faults in engine ECU. Probably some logged overheat fault. Clean it. This is standard TD5 behavior to switchnon the electric fan after overheat to protect the engine. "Drobek" = The Small One - Discovery 2, "Blufínek" = The Blue Thing - Defender 130, and for me at least Ford Mondeo Smile
Post #1061187 23rd Feb 2025 10:04pm
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grafty99



Member Since: 15 Aug 2012
Location: North Devon
Posts: 4796
United Kingdom 2002 Defender 90 Td5 HT Caledonian Blue
I can confirm as I've just had this on mine after a full rebuild. I must have had the ignition on at some point with the coolant sensor unplugged.

Any fault relating to the cooling system will make the ECU request AC fan until the fault is cleared. Erased all of the faults on mine and no more constant fan Thumbs Up 2002 90 Td5 Station Wagon
1990 Vogue SE
Triumph Tiger Explorer 1200
Td5 90 Thread http://www.defender2.net/forum/topic50767.html
Tdi 110 Thread https://www.defender2.net/forum/topic69562.html
RRC Thread http://www.defender2.net/forum/topic54492.html
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Post #1061258 24th Feb 2025 6:56pm
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landy andy



Member Since: 15 Feb 2009
Location: Ware, Herts
Posts: 5820
2006 Defender 110 Td5 USW Zermatt Silver
Thanks both for your input, but not the case for me. No faults showing on nanocom had checked it before but just checked again, and still clear.

Typically though, no fan running today.
Post #1061311 25th Feb 2025 10:47am
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landy andy



Member Since: 15 Feb 2009
Location: Ware, Herts
Posts: 5820
2006 Defender 110 Td5 USW Zermatt Silver
Noticed it running again today. Checked nanocom. Not ecu faults. But nanocom shows AC Fan requested. Even though all switches off.



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Post #1062048 5th Mar 2025 9:33am
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TexasRover



Member Since: 24 Nov 2022
Location: Paris
Posts: 1156
France 2002 Defender 110 Td5 DCPU Chawton White
There was a very recent discussion here I recall where a person had the AC fan running without there being a demand and it was concluded that after an overheat event the ECU plays it safe and kicks in the fan. I think was resolved by clearing the codes.

Does not explain the compressor though so maybe not going to be that simple.
Post #1062073 5th Mar 2025 2:28pm
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landy andy



Member Since: 15 Feb 2009
Location: Ware, Herts
Posts: 5820
2006 Defender 110 Td5 USW Zermatt Silver
Yes. That is correct, but I have no codes, and temps all read ok.


Puzzling
Post #1062096 5th Mar 2025 6:39pm
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bankz5152



Member Since: 02 Feb 2017
Location: South London/North Kent
Posts: 2195
2004 Defender 110 Td5 DCPU Epsom Green
Your coolant temp switch connected/working correctly?

The AC fan will come on if the ECU thinks theres even a chance of over heat, inc if the coolant switch is broken/ not connected. Instagram @defender_ventures
Empire Tuning - Agent
Post #1062103 5th Mar 2025 7:33pm
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landy andy



Member Since: 15 Feb 2009
Location: Ware, Herts
Posts: 5820
2006 Defender 110 Td5 USW Zermatt Silver
Yep temp gauge and temp on nano both all good.
Post #1062115 5th Mar 2025 8:35pm
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derbywill



Member Since: 25 Mar 2010
Location: Derbyshire
Posts: 561
England 2005 Defender 90 Td5 XS CSW Java Black
I had this recently and it was a dry joint in the air con control box that sits behind the 2 switches, I stripped the unit and re-soldered the joints and it was sorted.
But even if there isn't a fault showing in the ECU, clear the faults anyway, if it was an overheat it doesn't show a code but needs clearing to stop it.

Cheers
Will 2005 90 XS
1954 86'' Series 1 tilt
1968 88” 2A 200tdi
2002 110 Hardtop
Post #1062183 6th Mar 2025 12:59pm
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