How to check your fan resistors.

Ghianightmare · 25 Jun 2018

Great post, very helpful

thanks deMort.

Griffter · 26 Jun 2018

deMort said:
@ 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.

Delanor · 19 Aug 2018

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!

*
*
Del.

GMG · 12 Nov 2018

...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.

GMG · 16 Nov 2018

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

ballcock · 25 Nov 2018

Looks like RS are out of stock currently ...

Delanor , can you post a link to the ones you bought , or alternately would the below work? (They don't look particularly water proof!)

https://www.newegg.com/global/ie-en/Product/Product.aspx?Item=9SIA6705VF9527&ignorebbr=1

Robertb · 25 Nov 2018

if anyone is reading this with a view to fixing a turbo, 4s or 40 jahre then they have a different resistor (and fan assembly)

https://www.design911.co.uk/mobile/#part;id=7772

In my experience the only way of fixing those would be to drop the front PU, wheelarch liner and remove the fan in order to access the resistor.

GMG · 25 Nov 2018

...I ordered the last two because like a nitwit having successfully fitting the resistor and both fans now working at the same speed rather than one not working and the other working on full speed...wanting to water proof the connections I wrapped the resistor in gaffer tape which I am guessing was stupid given how hot they get?...so ordered another couple for when the new one dies prematurely and the other needs replacing...

diverzeusy · 23 Feb 2019

great posts, ive had my resistors over a year :dont know:
but as one fan was working fine I never got round to it, and forgot how, but this has relit the fire

thanks guys

youngsyr · 22 Jul 2020

Robertb said:
if anyone is reading this with a view to fixing a turbo, 4s or 40 jahre then they have a different resistor (and fan assembly)

https://www.design911.co.uk/mobile/#part;id=7772

In my experience the only way of fixing those would be to drop the front PU, wheelarch liner and remove the fan in order to access the resistor.

Bit of a thread resurrection, but I'm looking at replacing at least one of the resistors on my 2002 996 Turbo Tip in the near future and was wondering if there's an alternative to the £170 oem resistors?!

I found these two, which I think is the correct aftermarket resistor for the996 C2/4, but will it work ok on the 996 Turbo? :?:

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

https://www.ebay.co.uk/itm/0-5-Ohm-...568986?hash=item1a9b5acd5a:g:jzIAAOSwCxBe9LL4

Very useful thread, by the way. :thumb:

kurlykris · 22 Jul 2020

Looking at the schematics again ( I don`t have a 996 Turbo to test ) it seems that one fan resistor is 0.55 Î© and the other is 0.2 Î©, both would still be 100W max load :thumb:

I may be wrong, but zoom in on the attached picture of the fan wiring.

berni29 · 22 Jul 2020

Hi

I have just changed mine on my 986. I thought rather than do the aluminium ones, I would fit some ceramic ones like the originals. so I got a couple of these off of Amazon, (100w 0.5 ohm). They turned out to be a lot larger, but I wrapped them in self adhesive aluminium wrap and tucked them up under the front PU.

Great to have the low speed fans working.

Here is a pic of the resistor with some things showing its scale.

Berni

kurlykris · 22 Jul 2020

Berni29, you should not wrap wirewound resistors in anything, the whole point of them being open is to dissipate the heat, otherwise they will overheat and fail/possibly set on fire, they need the airflow to cool them

The aluminium alternatives should be directly mounted onto matalwork, preferably using a heatsink compound between them and the metalwork for the same reason, to dissipate the heat, these things get HOT, trust me I`m an electrical engineer, they are basically the same as a heating element in an electric fire :thumbs:

deMort · 23 Jul 2020

:agree:

Set them free young man

youngsyr · 24 Jul 2020

Can I just confirm that the prevailing opinion is to connect both fans to the resistor or just the high speed one?

I've read of people doing it both ways? :?:

How to check your fan resistors.

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