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landy andy

Member Since: 15 Feb 2009
Location: Ware, Herts
Posts: 5832

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?

23rd Feb 2025 3:26pm

MadTom

Member Since: 10 Sep 2013
Location: Olomouc
Posts: 642

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

23rd Feb 2025 10:04pm

grafty99

Member Since: 15 Aug 2012
Location: North Devon
Posts: 4796

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

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24th Feb 2025 6:56pm

landy andy

Member Since: 15 Feb 2009
Location: Ware, Herts
Posts: 5832

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.

25th Feb 2025 10:47am

landy andy

Member Since: 15 Feb 2009
Location: Ware, Herts
Posts: 5832

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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5th Mar 2025 9:33am

TexasRover

Member Since: 24 Nov 2022
Location: Paris
Posts: 1182

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.

5th Mar 2025 2:28pm

landy andy

Member Since: 15 Feb 2009
Location: Ware, Herts
Posts: 5832

Yes. That is correct, but I have no codes, and temps all read ok.

Puzzling

5th Mar 2025 6:39pm

bankz5152

Member Since: 02 Feb 2017
Location: South London/North Kent
Posts: 2200

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

5th Mar 2025 7:33pm

landy andy

Member Since: 15 Feb 2009
Location: Ware, Herts
Posts: 5832

Yep temp gauge and temp on nano both all good.

5th Mar 2025 8:35pm

derbywill

Member Since: 25 Mar 2010
Location: Derbyshire
Posts: 562

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

6th Mar 2025 12:59pm

landy andy

Member Since: 15 Feb 2009
Location: Ware, Herts
Posts: 5832

Interesting read. I’ve cleared the no code, and no change, so possibly the dry joint as you’ve had.

Did you get any pics of it whilst you were fixing it??

How easy is it to get too??

7th Mar 2025 8:15am

4RF RDS

Member Since: 19 Jul 2015
Location: Ottawa
Posts: 965

2000 Defender 110 Td5 XS CSW Epsom Green

Remove the speaker under the switch panel and you should be able to see it. Reach in and unclip it. Then gently pull on he wiring loom and reach in and unplug it.

Good luck

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7th Mar 2025 5:11pm

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