Radiator fan wiring

[twoqu]

Hopefully this might prove useful at least for those discerning 3B owners!. I was looking for some schematics to show how its all wired. Basically these two should cover it.
So in essence its three stage.

Stage 1 is the after run. This runs the fan through a resistance (0.9 ohms) to the fan first speed stage. This mean the fan runs at a lower speed than normal to save draining the battery after shutdown.

Stage 2 is the normal fan speed. A 12V supply is sent to the radiator temperature sensor. When the temperature reaches 95C the contact in the switch closes and sends the signal back up to the Stage 2 relay which closes sending a full 12V supply to the fan first speed stage. It will operate until temperature drops to 84C and the radiator switch contact opens.

Stage 3 is the full radiator speed. The 12V supply is switched through the radiator temp sensor when the temperature reaches 102C to the Stage 3 relay which closes sending 12V back to the radiator fan second speed stage. It will operate until temperature drops to 91C and the radiator switch contact opens.

On cars with A/C, switching on also causes the fan to run. I believe this is at the Stage 1 speed. Still looking for the schematic for that but it must run the fan through the resistance as per the after run.

According to ETKA the 3B fan is rated as either 350/250W (P/N 165 959 455AE) or 350/150W (P/N 431 959 455A)with a 305mm diameter fan which may or may not be a typo! I would think it is likely to have a 250W second stage than a 150W. It has three connections. One is for ground, the others being the power feed for either of the two stages.

On later cars with the resistor pack the fan speed is controlled by the 3 different resistances rather than fan stages. The later fan is a 500W single speed I believe. It looks like this was stolen wholesale from the later 200q, thats why the fan has a 443 p/n!

Therefore some simple tests to prove function of the various stages would be:
1: Connecting the after run temp sensor wires together should make the fan run on the first stage fan speed which is less than the full power first stage fan speed.
2: Bridging the radiator temperature sensor connector from the terminal with power on to the other terminals should cause the fan to run at the respective fan speed.

As it looks like the radiator switch is fed by a fuse, then clearly no power at the switch would cause inoperative fan stages other than the stage 1 after run or A/C.
If the switch contacts do not work you would loose either/both fan stages.
Other issues would need to be tested using the schematics to check for power/signals at the relevant places.

Its not impossible for either fan speed to die or other issues such as sticky relays causing the fan to run all the time.

[SteveH]

Thanks for the research Robin, that will make fitting my new fan wiring a whole lot easier. I'm going to see if I can get more than one speed out of the replacement.

[twoqu]

No problem. I was trying to work it myself as thats on the cards for me as well.
To be honest you will only get two decent speeds with (no surprise!) a dual speed fan! There are aftermarket and OE ones available. With something like the Pacet I can only see you getting the after run speed and a full speed when connected to the lower temperature switch or one speed on the high temperature switch and no after run.
As other have not experienced a problem and I have only heard a fan on the highest setting about 3 times in 15 years of Audi ownwership, perhaps its not an issue!
The other issue if I have read it correctly is that if the power supply to the rad switch dies you lose both stages. Its a 25A supply which sounds pretty meaty so again perhaps nothing to worry about. I think when I looked at this before, Audi had pretty much used all the best practice in the cooling department apart from the rad capacity!

[AndyP]

No problem. I was trying to work it myself as thats on the cards for me as well.
To be honest you will only get two decent speeds with (no surprise!) a dual speed fan! There are aftermarket and OE ones available. With something like the Pacet I can only see you getting the after run speed and a full speed when connected to the lower temperature switch or one speed on the high temperature switch and no after run.
As other have not experienced a problem and I have only heard a fan on the highest setting about 3 times in 15 years of Audi ownwership, perhaps its not an issue!
The other issue if I have read it correctly is that if the power supply to the rad switch dies you lose both stages. Its a 25A supply which sounds pretty meaty so again perhaps nothing to worry about. I think when I looked at this before, Audi had pretty much used all the best practice in the cooling department apart from the rad capacity!

Found this thread looking for answers to the same question, thanks again Robin

[s2driveruk]

Bit of a gem...made it sticky. After the thread resurrection

[Tom_]

Basically, the 12v feed for the fan is going through only when the temp across a certain value? I have a SPAL fan because of no room there and I initially wanted to reuse stock wiring (feed and ground for the fan). I am not sure how the system completely works, but I would say the fan isn't powered all the time.
Or i am understanding that incorrect? I have 7A CQ

edit : It looks to me like the fan gets the power either from a low-speed relay or high-speed relay. The speed will depends on which relay gives the fan power.

[johne]

Both for the 3B and later cars with the single speed radiator fan motor the wiring is different for cars with AC and cars without AC.

The current flow diagram in post #1 is for a car without AC. F18 and F54 sit in a unit together that is screwed into the bottom of the radiator and trigger the medium and high speeds respectively of the radiator fan depending on the temperature of the coolant as it leaves the radiator. F18 and F54 do this by switching a +12volt feed to the relays that operate the radiator fan motor.

The current flow diagram in post #6 is for a car with AC. Here F18 and F54 work in the same way just that instead of switching +12volts to the fan relays they switch to ground.

The radiator fan motor does not run all the time, it only runs when triggered by F18 or F54, or by the After Run control unit. On cars with AC, the radiator fan will run at low speed whenever the AC is turned on and at medium speed triggered by the AC refrigerant high pressure switch.

[Tom_]

I would say that the diagram posted by me isn't for the car with AC but without AC, as there are mentioned AC unit, but only on a few things and these connectors where the AC is mentioned, could be not populated.
There is a continue of the second page for that Fan
That diagram from post #1 seems a little bit weird to me

[johne]

The diagram in #1 is a genuine current flow diagram from Audi so can't "look weird" and is correct for a European car without AC.

The diagram in #6 that you posted is from the Robert Bentley US produced Official Factory Repair Manual for US cars. If you have that manual you'll see that there's a progression of wiring arrangements between 1988 and 1992 starting with F18 and F54 switching to +12 volts to by 1990 switching to ground as shown in diagram 19-10-20.

[Tom_]

yes, you are correct, but diagram below suits the 7A without AC the most I would say. I noticed on 3 pin thermoswitch on rad, there connected only two pins...the middle one is not populated in the connector

[Tom_]

diagram