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Old 5th October 2019, 15:32   #21
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Originally Posted by SD1too View Post
What is the precise nature of the fan fault which you are considering?
I was referring to stocktake's surprise that a faulty 3-speed fan pulsed from aircon demand:

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It definitely cycled on and off I have never known another 3 speed fan do this, looking back it was certainly not a high speed.

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Old 5th October 2019, 17:50   #22
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I was referring to stocktake's surprise that a faulty 3-speed fan pulsed from aircon demand
My explanation for that is in post no. 17, with which Stocktake concurs. However it wasn't stated that the air con. was activated at the time.

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Old 6th October 2019, 10:19   #23
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I hadn't thought about it before, but isn't fan cycling logical for all motors?


Why would a faulty 3-speed fan run at a higher speed to cool the condenser but not trip off when the trinary pressure dropped? The implication is a faulty 3-speed would run continuously at higher speed while ever the aircon was in use.



TC
Hi TC, it is my understanding that the low and middle speeds use the same neg brush. hence this appears to wear first. when it fails it then takes out low and medium together hence no cycling.
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Old 6th October 2019, 12:02   #24
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Hi TC, it is my understanding that the low and middle speeds use the same neg brush. hence this appears to wear first. when it fails it then takes out low and medium together hence no cycling.

Indeed, but the situation with Pab's car had the aircon fan pulsing at the (low) brush-wear compromised 'medium' speed. Which though unusual is logical.
In the OP's case, the aircon fan is running continuously at some speed or other, yet the low and medium speeds have, apparently, failed. The high speed motor brushes are proviing some engine cooling at 112C, so what mechanism is switching them in for the aircon demand?


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Old 6th October 2019, 12:18   #25
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Indeed, but the situation with Pab's car had the aircon fan pulsing at the (low) brush-wear compromised 'medium' speed. Which though unusual is logical.
In the OP's case, the aircon fan is running continuously at some speed or other, yet the low and medium speeds have, apparently, failed. The high speed motor brushes are proving some engine cooling at 112C, so what mechanism is switching them in for the aircon demand?


TC
Indeed a strange one.
I can recall a different members car 2.5 v6 and that had symptoms of when the A/C was switched on there was a slight delay of 10 to 15 seconds before the fan started on a slow speed with no pulsing on and off. I thought twas a most unusual action until I opened the relay box to find a pcb .

But back to the case in hand, if this is the correct fan and relay then what is happening would indicate a lack of signal from the ecu to the relay box wouldn't it? Yet the temp sensor must be working to allow THE OBD to show temps???

Hope dave6 comes back with more info so we can help diagnose this one, it's interesting
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Old 6th October 2019, 15:51   #26
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The high speed motor brushes are proviing some engine cooling at 112C, so what mechanism is switching them in for the aircon demand?
The air conditioning doesn't trigger fast speed on a 3 speed system, only low and medium.
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Hope dave6 comes back with more info so we can help diagnose this one, it's interesting
Dave; I gave my diagnosis in post number 10. I believe that it's the usual case of the earth brush common to low and medium speeds failing. This is because Dave6 reported that in 'Econ' mode the fan ran as soon as the coolant temperature reached 112 degrees.

But Dave6 proposes to replace his 3 speed system with a 2 speed so my hypothesis will never be tested.

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Old 6th October 2019, 16:04   #27
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The air conditioning doesn't trigger fast speed on a 3 speed system, only low and medium.
Exactly, so what's tripping the fan when the aircon's on?
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Old 6th October 2019, 17:20   #28
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Exactly, so what's tripping the fan when the aircon's on?
I've just reviewed all Dave6's posts and I now see what you're getting at. He says that the low and medium speeds don't run with air con. off but low speed does work with air con. switched on (demist test). I don't see how that can be possible unless Bodger Man has been at it, like this:
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... until I opened the relay box to find a pcb


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Last edited by SD1too; 6th October 2019 at 18:01.. Reason: Further consideration
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Old 12th October 2019, 22:00   #29
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Thanks for the help all. I am pleased to report that my car has a new two speed fan thats working beautifully. Low speed comes on at 99 and turns off at 95. Low speed comes on with the demist test and with air con. It's good to have my V6 growls back! All plenum drains checked.

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Old 13th October 2019, 07:28   #30
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Thanks for the update Dave.

We'd all be very interested to know what is inside your original control box. Could you remove the lid please and let us know whether you see just three relays and wiring or a printed circuit board as well.

Many thanks.

Simon
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