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deMort
Zolder


Joined: 21 Mar 2015
Posts: 5533
Location: Brighton


PostPosted: Mon May 07, 2018 7:10 pm    Post subject: How to check your fan resistors. Reply with quote

Youll need a voltmeter and a wire pierceing end .. if not then a small cut into the wires with a blade to access the copper.

You will need tape to seal the wires after so a probe is best .. see image .

Over view of the system ..

A/C turned on and the low speed fans will be operated , it doesnt matter if the a/c is out of gass .. the car doesnt care .. it will still increase the engine rpm and turn on the low speed fans .

Low speed fans will kick in reguardless at an engine temp of about 95 C .

High speed fans will kick in at an engine temp of about 105 C .

3 wires on the resistors ..

One goes to the fan motor
One comes from the Low speed relay
One comes from the high speed relay.

The high speed by passes the resistor in that steel caseing .. it goes straight to the fan.

You dont need to know which wire is which but there is a diagram below if you want to look .. dont help much as the colours of the resistor are white , white/green and green which it doesnt show .. lol .

Engine running , a/c turned on then check each wire for 12 volts .. if the resistor is working then x2 of the wires will have a feed and the fan will be turning ... if the fan isnt turning then you have a faulty fan motor.

A Failure of the resistor will mean you only have feed on x1 wire .. no output to the fan motor .

You can replace the resistor with non porsche that are listed in other posts .. perhaps someone could add a link here for me .

If replaceing with a Porsche one then you can either strip out the arch liner or you can cut and join .. soldering iron will be required along with heat shrink and tape .
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alex yates
Brands Hatch
Brands Hatch


Joined: 06 Mar 2014
Posts: 14476
Location: The Ribble Valley, Lancashire

2000 Porsche 996 Carrera 4

PostPosted: Mon May 07, 2018 7:25 pm    Post subject: Reply with quote

Ballast resistor:

https://uk.rs-online.com/web/p/panel-mount-fixed-resistors/0188071/?searchTerm=188-071&relevancy


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deMort
Zolder


Joined: 21 Mar 2015
Posts: 5533
Location: Brighton


PostPosted: Mon May 07, 2018 7:32 pm    Post subject: Reply with quote

Blimy .. this post got very fat all of sudden Floor
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alex yates
Brands Hatch
Brands Hatch


Joined: 06 Mar 2014
Posts: 14476
Location: The Ribble Valley, Lancashire

2000 Porsche 996 Carrera 4

PostPosted: Mon May 07, 2018 9:51 pm    Post subject: Reply with quote

My fault mate, posting a mega long link.
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Jamesx19
Spa-Francorchamps


Joined: 10 Jul 2015
Posts: 374
Location: Brighton


PostPosted: Mon May 07, 2018 10:23 pm    Post subject: Reply with quote

Good post demort.

To get the correct reduction in fan speed (low speed circuit goes through the resistor) it needs of be about 0.5 K or 500 ohms

The other important thing is the power capacity of the resistor. The car only runs 12 volts, but even a draw of 5 amps will give 60 watts.

As per Alex's earlier post and link, that it the one you need. And a lot cheaper than a genuine one it is too....
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infrasilver
Fast & Furious
Fast & Furious


Joined: 04 Oct 2010
Posts: 7908
Location: East Midlands

2001 Porsche 996 Targa

PostPosted: Mon May 07, 2018 10:23 pm    Post subject: Reply with quote

alex yates wrote:
My fault mate, posting a mega long link.


Very untidy Mr Yates Hand you can just post the first part of the link. (one of my editing pet hates, overlong links) frustrated
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mikealdren
Newbie


Joined: 06 Sep 2016
Posts: 10



PostPosted: Tue May 08, 2018 7:31 am    Post subject: Reply with quote

Jamesx19 wrote:
Good post demort.

To get the correct reduction in fan speed (low speed circuit goes through the resistor) it needs of be about 0.5 K or 500 ohms

The other important thing is the power capacity of the resistor. The car only runs 12 volts, but even a draw of 5 amps will give 60 watts.

As per Alex's earlier post and link, that it the one you need. And a lot cheaper than a genuine one it is too....


Hi guys,
500Ω or 500mΩ as per Alex's post? I think Alex is right, 500Ω would only need about 0.3W at 12V.

thanks
Mike
 
  
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Jamesx19
Spa-Francorchamps


Joined: 10 Jul 2015
Posts: 374
Location: Brighton


PostPosted: Tue May 08, 2018 9:06 am    Post subject: Reply with quote

Errr yep sorry math's wrong! 500 m ohms or 0.5 ohms not 0.5K!!!

Basically drop the voltage which drops the fan speed. Apologies for the poor post above.
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mikealdren
Newbie


Joined: 06 Sep 2016
Posts: 10



PostPosted: Tue May 08, 2018 3:22 pm    Post subject: Reply with quote

No problem, I just noticed the anomaly and thought I ought to warn the unsuspecting...
 
  
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alex yates
Brands Hatch
Brands Hatch


Joined: 06 Mar 2014
Posts: 14476
Location: The Ribble Valley, Lancashire

2000 Porsche 996 Carrera 4

PostPosted: Tue May 08, 2018 3:58 pm    Post subject: Reply with quote

infrasilver wrote:
alex yates wrote:
My fault mate, posting a mega long link.


Very untidy Mr Yates Hand you can just post the first part of the link. (one of my editing pet hates, overlong links) frustrated


Embarassed

I must not post mega long links, I must not post mega long links, I must not post mega long links, I must not post mega long links, I must not post mega long links, I must not post mega long links.

wack

Cheers Chris. Thumb
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maldren
Österreich


Joined: 07 Oct 2016
Posts: 941



PostPosted: Fri Jun 22, 2018 7:53 am    Post subject: Reply with quote

Just fitted cheap Chinese resistors off ebay (sorry can't fine the thread to credit who found them), £3.38 a pair and they arrived in about 2 weeks.

The old resistors had failed. The green/white lead goes to the fan and the green and white lines are the two inputs. On mine, testing the resistor with a meter showed the white was connected to the green/white but the green didn't connect to anything else. On this basis, I assume that the white line is the full power and the green is low power input to the failed resistor.

The wiring was quite brittle and the wires quite short so I decided to solder extension wires to the resistor, the fuse is 40A so it looked like I needed some heavy cable (4mm²) to match what's there but it's hard to find. Clearly the fans don’t really draw 40A each so I looked at various 3rd party fans and found that they typically draw about 5A and the low speed will draw less than the full power. I decided that it's only a few inches long and I used 13A mains flex.

I then needed a more heavy duty soldering iron! I joined the White and Green/White cables to one side of the resistor and the Green top the other, covered with heat shrinking cover. I looked at screwing the resistors in place but they fit conveniently into one of the clips from the original resistors.
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2003 996.2 C2 Coupe Arctic Silver
 
  
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Griffter
Monza


Joined: 22 May 2016
Posts: 226



PostPosted: Mon Jun 25, 2018 6:29 am    Post subject: Reply with quote

I understand the low/high fan speed and a/c on/off thing. I had assumed the fans would engage instantaneously when the a/c is switched on but they don’t on my car. Neither do they switch off instantaneously when when the a/c is turned off. For years I had wondered whether my fan resistors were fubar, but the a/c blows cold and the engine temp gauge doesn’t normally pass the centre, so I never worried too much. But having observed the behaviour over spring and into summer this year, there seems to be more to it than just a/c on = fans on. The fans seem to be controlled by an ecu and their operation to depend on cabin temp and possibly ambient temp.

On my car there is a delay between switching the a/c on and the fans running. Yesterday it was about 5-10 seconds at a guess. From memory the delay seems to depend on the cabin temperature. If it’s cold, I’m sure sometimes they don’t come on for quite a while (haven’t been able to confirm this recently!).

The engine temp gauge sits bang in the middle in normal operation and if it does rise, eg in traffic, the fans comes on at the same speed as they do when the a/c is on. I have never experienced them coming on at a higher speed.

Is this normal?! Am I overthinking it?!
 
  
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Daniel
Donnington
Donnington


Joined: 02 Feb 2005
Posts: 11977
Location: Not where I want to be!

2000 Porsche 996 GT3 Mk1

PostPosted: Mon Jun 25, 2018 8:22 am    Post subject: Reply with quote

Unless its cleaning/detailing me and DIY things on cars is a no no!

Is this something an Indy could do or someone around Gatwick who could show me for a beer? Thumb
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maldren
Österreich


Joined: 07 Oct 2016
Posts: 941



PostPosted: Mon Jun 25, 2018 8:34 am    Post subject: Reply with quote

Daniel wrote:
Unless its cleaning/detailing me and DIY things on cars is a no no!

Is this something an Indy could do or someone around Gatwick who could show me for a beer? Thumb


PM sent
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2003 996.2 C2 Coupe Arctic Silver
 
  
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deMort
Zolder


Joined: 21 Mar 2015
Posts: 5533
Location: Brighton


PostPosted: Mon Jun 25, 2018 11:17 am    Post subject: Reply with quote

@ Griffter

Yup thats normal .. the fans switch on to cool the a/c refrigerent , the compressor will need to run for a bit before it needs any cooling.

Likewise the fans will run for a bit after the a/c is switched off as the gass is still hot.

The resistors either work or dont work.

The control unit is the heater panel and the dme .

No high speed just means the coolant has never reached approx 105 degrees whilst you have been listening .. it is just about possible there is a fault but im pretty dubious that there is ..

The only test is to connect a laptop and drive link them .. turn them on basically .
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Ghianightmare
Monza


Joined: 25 Apr 2017
Posts: 174
Location: Dublin


PostPosted: Mon Jun 25, 2018 11:25 am    Post subject: Reply with quote

Great post, very helpful

thanks deMort.
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Griffter
Monza


Joined: 22 May 2016
Posts: 226



PostPosted: Tue Jun 26, 2018 6:03 am    Post subject: Reply with quote

deMort wrote:
@ Griffter

Yup thats normal .. the fans switch on to cool the a/c refrigerent , the compressor will need to run for a bit before it needs any cooling.

Likewise the fans will run for a bit after the a/c is switched off as the gass is still hot.

The resistors either work or dont work.

The control unit is the heater panel and the dme .

No high speed just means the coolant has never reached approx 105 degrees whilst you have been listening .. it is just about possible there is a fault but im pretty dubious that there is ..

The only test is to connect a laptop and drive link them .. turn them on basically .


Excellent, thank you.
 
  
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Delanor
Nürburgring


Joined: 01 Oct 2016
Posts: 428
Location: The land of the big cat!


PostPosted: Sun Aug 19, 2018 7:38 pm    Post subject: Reply with quote

Having discovered that neither radiator fan was working after the N/S radiator sprung a leak, the OE replacement fan resistors are approx` £170 a pair (no thanks) so an equivalent resistor pair (100watt 0.5 ohm) were sourced for £3.38 which were mounted on some 15mm diameter tube with some new connectors soldered on.

These are easy to fit and even easier to replace - they work a treat!

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GMG
Monza


Joined: 07 Jan 2018
Posts: 200
Location: Devon


PostPosted: Mon Nov 12, 2018 6:27 am    Post subject: Reply with quote

...having removed my front PU for a repaint and cleaning the rads I noticed that my passenger side fan does not work when air conditioning is on leading me to think that the fan resistor is fubar ...

I followed this helpful link and ordered the ballast that Alex posted...

Please can someone advice me how this is connected?

Thank you.
 
  
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GMG
Monza


Joined: 07 Jan 2018
Posts: 200
Location: Devon


PostPosted: Fri Nov 16, 2018 9:18 pm    Post subject: Reply with quote

...all done and fans working properly...cheap fix!
 
  
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