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Discussion Starter · #1 ·
The cooling fan on my 1995 Aero is not switching on: fan motor is ok, relay is ok. The fan operates a few seconds after the a/c is switched on, regardless of the engine temperature. There is no radiator switch on post-94 9000's, so I guess the fan is triggered by the temp sensor in the block? ALl the usual sites only have info about pre-94 cars, and my Haynes manual is useless. Anybody got a wiring diagram for these cars?
 

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Yup, the same fan is also used to cool the A/C rad, so if you ever get a problem with the fan not coming on, turn the AC on to full.

And yup, the cooling fan for the coolant is controlled not by a radiator switch but by the ECU. BillJ knows a bit more about it I think.

Is that car actually overheating Richard? Have you tried starting it, leaving to to idle for some time and seeing what happens? The temperature gauge is also controlled by the ECU, not the direct reading from the block of earlier models.
 

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Bu66a!

Well at least we're a step further down the diagnostic road


I'm afraid I don't know much more, but following a logical train of thought, I presume then that the needle is entering the red on your temp gauge, which indicates that at least the ECU is getting the signal. It's unlikely to be an ECU failure and I would suspect a poor connection somewhere the the circuit between the ECU and fan- but you've probably sussed that anyway. I'm pretty certain there's only one relay that controls the fan, so if it's working for the ACC, it's not a relay problem. Now I really am stuck so I'll shut up...
 

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The cooling fan is not controlled by the ECU but by the EDU (Electronic display unit), which is the computer that calculates mpg, etc. on your instrument display. The engine coolant-temperature sensor (ECS,an NTC resistor) communicates to the EDU control computer. The computer calculates the coolant temperature from the resistance and uses the info to control steps 1 & 2 of the 2 speed fan. I have a wiring diagram but no scanner to show you the circuits. Maybe this'll help: the ECS is on the cylinder head. It gets connected with a yellow and orange wire to pins 34 & 27, respectively, on the EDU (you'll need to remove the top dash cover and remove the instrument panel). The EDU sends output to appropriate relays and the 2 speed fan through two wires: a blue wire at pin 5 and a blue/white wire at pin 6 on the EDU. The blue wire is for the AC fan, and the blue/white goes to the 2 speed fan.
 

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Discussion Starter · #8 ·
Thanks Robert! Funny thing is, although I have air con, there is only one fan, and it is definitely single speed. And this one fan doesn't even draw air across the a/c condenser...I'm really confused - how does the air con dissipate the condenser reject heat when the car is standing still - the single fan cannot be much use!
btw, did you get this info from a Saab workshop manual?
 

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Sorry Rich for not getting back quicker - I could be wrong, but I think it doesn't matter whether one has the single speed fan or the 2 speed fan. The principle of operation should be the same. I would guess that the only difference, seeing as you have no AC fan, is that there will be no blue/white wire emanating from the EDU on pin 6. I'm sure the wiring is there for an AC fan, and I bet there's a mount plate for one on your condenser. I can't understand why Saab would feel it unnecessary to include an AC fan on UK models, yet provide one on US versions. Maybe the previous owner removed it? Mine comes on whenever the AC is switched on. Oh, I have the Saab electrical schematics for all '94 vehicles, and some schematics for OBDII vehicles.
 
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