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Cooling fan resistor

Hi Team,

So, in tracing down a cooling fan issue that manifested itself from MOT man knocking off wires to cooling fan yesterday....!....I tested it as per Clarks to trace problem. I jumpered the leads to the fan and it came on in fast mode with the ignition on however with ignition off and wires still jumpered there was no slow cooling fan speed. I bench tested the relay as per Clarks and all checked out fine. Fan comes on when engine running and temp going into the red as per normal.....just not on slow speed when engine off and hot.

So I think I may have an issue with the cooling fan resistor. Only had car for 10 months but I don't ever remember the cooling fan coming on slow speed after a hot run with engine off...but evidently it should.

Is there an obvious/simple (cheap?!) fix for this? Mine is a RHD 924S 1988.


Thanks in advance,

M
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Old 01-10-2019, 04:21 AM
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If you jumpered the leads to the fans you are probably bypassing the cooling fan resistor that provides slow speed operation. Without bypassing, if you are not getting slow speed operation, and you are certain the car has reached a sufficient temperature to activate the relay to slow speed, then it’s more likely that the coolant temperature switch in the radiator has failed. Btw the slow speed resistors rarely fail, they are robust, heavy duty wire would ceramic resistors. What usually fails is the wiring to/from those resistors, they get very hot and the insulation melts over time. If it’s isnt the temp switch you should check the wiring by the resistors.
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1986 944 (Street); 1986 944 (Track); 1986 951; 1989 951 (3.0L 8V); 2000 996 Cab.
Old 01-10-2019, 05:41 AM
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Thanks for reply........are you saying the engine has to be hot when you jumper the connections for slow speed? I thought you could jumper them from cold and then the slow speed fan would kick in...as per Clarks? When I turn ignition on the fan comes on at full speed without jumping.....
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Old 01-10-2019, 06:17 AM
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Quote:
Originally Posted by mikseymono View Post
Thanks for reply........are you saying the engine has to be hot when you jumper the connections for slow speed? I thought you could jumper them from cold and then the slow speed fan would kick in...as per Clarks? When I turn ignition on the fan comes on at full speed without jumping.....
Depends which connections you are jumping. If you jump from the fan fuse to the fan you won’t ever get slow speed, only fast. If you jump from the slow terminal on the relay to the fan, you’ll only get slow speed if the temp switch calls for it, so the engine must be hot enough to trigger it, otherwise you won’t get anything.

If you are following Clark’s you should be fine, but like I said in most cases it’s not the resistors that cause issues, it’s the temp switch or wiring you should look at first in that order.
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9TECHNIK | TRANSAXLE ÄRA
1986 944 (Street); 1986 944 (Track); 1986 951; 1989 951 (3.0L 8V); 2000 996 Cab.
Old 01-10-2019, 06:36 AM
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Replaced with working 2nd hand unit...and now all works as it should! Other than staying on when it is triggered by a certain temperature for a time when ignition turns off...are there any other times it comes on?

Thanks.

M
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Old 01-18-2019, 08:47 AM
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