A very common failure on the 993 is the failure of the systems controlling the fans in either front wing for the oil cooler (RH side) and air conditioning condenser (LH side). There are a variety of components in the systems such as control units, temp sensors, relays etc, which can make the system fail totally, but the most common failure is in the circuits controlling slow speed fan operation.
With the oil cooling system, there is first a thermostat controlling flow to the cooler once the oil warms up (>83C). Then a temperature sensor will inform the control unit if the oil gets to 110C in order to start the fan in slow speed. High speed will be called if the oil gets REALLY hot, around 125C ! The top marking on the oil temp gauge is around 150C, next down approximately 120C, so any reading above 9 o’clock on the gauge should have the fan running without fail.
The A/C Condenser fan should start in slow as soon as A/C is turned on, trigger for high speed unknown (to me at least).
The usual failure is for the fans to only run in fast – this evidences itself with the fan kicking in for just a few seconds when the oil (or refrigerant) is very hot. Unless you sit in traffic regularly you may not experience this, but basically it allows either system to get too hot before something is done about it.
Fortunately, you don’t need a Bosch ‘Hammer’ or a BSc in Electrical Engineering to check the system. The oil cooler fan is controlled by relay R04, A/C by R14 – these are in the fuse box above the RHS of the fuel tank. The photo shows R14 in, R04 removed (white socket). Note that Porsche sourcing still includes VW parts bins !
The quick check is to test fan operation by simulating the hot conditions - remove both relays, and then take the cap off one, as in the picture below. Easily done by just easing the tabs out…. there are actually two relays inside, the top one for slow speed (fan in series with resistor), the lower one for fast (12V across fan, no resistor).
The relays are identical, so re-install the disrobed relay in either socket – the oil cooler one is the RH socket (from the front). Now find yourself something to prod with (I used the other end of an artist’s brush) – and switch the contacts over. A relay is just an electrically operated switch, and the pic shows the contacts, which change over when the relay is energised. So you just have to do the energising – the circuit is live without ignition. For low speed, insert your prod under the plate the contacts are mounted on, and lift slightly until you see the contacts change over. You should hear the fan start - it’s not quiet, even in slow. For the high speed test that relay is mounted with the contacts towards you, so just push your prod against the relay contact plate. A minor hurricane should occur near your foot !
Now remove the bare relay, insert in other socket, and repeat the test.
If fast works but slow doesn’t, its 99% sure your slow speed resistor is toast. With an ohm-meter (DVM) you can measure the circuit – with relay removed, measure between 5 and 7 on the appropriate socket. Yes I know you can’t see the numbers, but they correspond to 87 and 87C on the relay, which you can see, and then relate to the socket. If you’re still not sure, they are the front centre and left lower contacts in the socket (looking from the front). Do be careful, as some of the socket contacts have 12V on them (2&3) and you could hurt your meter or a fuse. The resistance should be <1 ohm, my nice new ones are around 0.7, where they were >1K ohms before.
I got OPC Silverstone to do mine under warranty - it took them 2 hours, including a good ‘hammering’ to confirm my diagnosis, but I suspect they have done a few ….. happily they were able to fit me in before my trip to Goodwood and consequent long periods in traffic. An OPC or specialist should be able to diagnose this without heat soaking the car – so make sure you tell them not to do it!
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