Cooling fans not kicking in

Hi all I've just had a low temperature thermostat(71c) and new expansion tank fitted to a 2001 gen 1 996 and the mechanic has noticed that the cooling fans are not kicking in even if the air con is on they won't run.. The fans will operate so it not a failure of the resistors or the fan motors.. Fuses have also been checked.. is there a relay that could have failed ? Any suggestions as to what the problem might be.. The expansion tank was nearly empty and appeared to have dried coolant residue on the outside of the tank when it was removed from the car so I feel the fans had stopped operating before the car was dropped off at the garage.. Thanks Johnny

It sounds like your ballast resistors have failed. It's a relatively common issue. eg, See -> http://www.911uk.com/viewtopic.php?...s=0&postorder=asc&highlight=ballast+resistors

As suggested the resistors are the most likely culprit but you can test the relays as below. Drivers footwell. 5 relays marked '53' Left to right #1 not involved #2 left side low speed #3 left side high speed #4 right side low speed #5 right side high speed If the resistors are blown then the low speed won't work but the high speed still will be ok. Seems unlikely that all the relays would have failed but this will at least confirm the operation. Should work with the ignition off if I remember correctly.

Are they not just for low speed? AC on should trigger high speed, shouldn't it? That's how my 98 C2 works.

As stated in my original post the fans are working when tested.. The near side is working in low and high speed.. The off side is running only on high so the resistor has failed so need's replacing that side The problem is the fans are not cutting in on either speed when the car gets up to temperature or when the air con is switched on

As previously stated .. if you bridge out term 30/87 on the low and high speed fans you will see if the fans , resistors and wiring from relays to them is ok . You would then fit a donner relay to prove that .. a/c on , low speed relay. You would then check the feed/earth on term 85/86 to each relay .. You will only get this with either the a/c switched on for the low speed ( 95 degrees ) .. or an engine temp of 105 or higher for the high speed .... One of the above will Not work . Considering you have a low temp stat fitted i kinda doubt you will get the car hot enough to reach this high temp. If you are relying on the temp gauge to give an accurate reading .. then it doesnt .. you need a tester to see the Actual engine temp . Wiring diagram is below which i have taken from the Link T8 posted .. i gave details about the system there . Are you fault finding this or is a garage ? How did you test the fans ?

Link to how to replace Ballast Resistors: https://911uk.com/porsche/ballast-resistor-replacement.67488/#post-722718

Hoping this may help someone with the same problem that I had. The low speed and high speed cooling fans were not working on the passenger side (left), but were working on drivers side. I checked the fuses and relays by swapping them over, but still not working on passenger side. I then did some more reading on these forums and found someone who stated that if both low and high speed fans are not working, it's probably the fan that has failed. So I fitted a new fan kit that includes the resistor for Heritage and it's now working fine.

I just got round to fitting two Arcol RS resistors as my left low speed fan had failed, so did both sides at the same time (thanks to Gixxer996 for the spare resistors). Not a bad job, cleaned up the metal and used some thermal paste between the resistor and the fan mount, drilled a couple of holes and bolted through, then after the picture a bit of satin black paint on the remaining bare metal and blobs of lanogard motogrease on the nuts and bolt heads, all worked great!