Radiator Fan Issues - Running on ignition - Help

[Trist28]

Firstly apologies - I'm not great with electrics, please bear with me. I have read a thread on here regarding fans running full time https://www.s2forum.com/forum/techni...nstantly-s2-93 etc - however mine is running when I turn the ignition on, and stays on whilst the car is running. Switch ignition off it stops.

Its a 1993 non AC ABY Avant

I've checked all the fan relays and they seem fine
I've run the test of the after-run system and that fires up on ignition for 5 seconds as it should so assume the 324 relay is good.
I've tried another rad temp sender

Will the 2 blade sender on the water manifold that you cant really get to without taking the rad out cause this? Any ideas appreciated. Or anyone nearby fancy taking a look for me for beers / notes?

[Mikes2]

Afterrun fan circuit only works with engine and ignition off. Your fault lies in the speed 2 and 3 function. Disconnect the wiring from the fan switch at the base of the radiator - your fan will probably stop. Measure the resistance on the fan switch. A low reading means you need to replace the switch.

[S2central.net]

Yep - go after the thermal switches at the bottom of the rad first... those determine which of the two main fan relays are activated (speed 2 or speed 3). Its possible a relay is stuck on - or the switch wiring is shorting. I do recall the wiring down there is dirty & brittle so care is advised when pulling off connectors etc

The 2-pin thermal switch in the water rail is only for the after-run activation (the water recirculation pump combined with fan speed 1).

[Trist28]

Cheers both. Ill get onto this tomorrow and report back.

[Trist28]

Afterrun fan circuit only works with engine and ignition off. Your fault lies in the speed 2 and 3 function. Disconnect the wiring from the fan switch at the base of the radiator - your fan will probably stop. Measure the resistance on the fan switch. A low reading means you need to replace the switch.

Hey Mike - Unplugging the fan switch in the radiator made no difference, fan still runs on ignition. I have re-tested all the relays on the bench and they function perfectly. The rad fan switch itself - I tested what I thought is 'ohms' and get low reading, but that is the same on about 8 spare rad switches I have from other audis so assume I'm doing something wrong rather than they are all dead?

[Trist28]

Yep - go after the thermal switches at the bottom of the rad first... those determine which of the two main fan relays are activated (speed 2 or speed 3). Its possible a relay is stuck on - or the switch wiring is shorting. I do recall the wiring down there is dirty & brittle so care is advised when pulling off connectors etc

The 2-pin thermal switch in the water rail is only for the after-run activation (the water recirculation pump combined with fan speed 1).

Hi Paul - See my post above. Would it suggest a wiring fault? Oh I've PM'd re wiring diagrams on B3s

[Mikes2]

check the resistor pack and associated wiring

[S2central.net]

Attached is a little 8-page primer with the schematic marked up and a lot of notes to help anyone fault finding this circuit. I did it quite quickly so please forgive any typos, but do let me know if you find serious errors. By following the logic of this - pretty simple relay stuff - you can quickly find ways to isolate faults in specific relays, but a basic multimeter will be very useful for any tests.

[S2central.net]

Another note to add with regards that 'engine running only' pin onto J155 is the corner case where it gets activated by the ECU for a few seconds (via the T5h plug which tracks to pin 41 on the ECU) when the ignition is turned on - this is why you hear the after-run water pump being tested for a few seconds - all part of the control circuitry inside J155.

[S2central.net]

Hey Mike - Unplugging the fan switch in the radiator made no difference, fan still runs on ignition. I have re-tested all the relays on the bench and they function perfectly. The rad fan switch itself - I tested what I thought is 'ohms' and get low reading, but that is the same on about 8 spare rad switches I have from other audis so assume I'm doing something wrong rather than they are all dead?

This possibly means you have a short circuit on the wiring plug to the radiator fan switches. That is a 3-pin plug and with ignition ON, you should only see 12V at pin 3 (blue/red wire). With the connector unplugged from the switches it would be worth testing for volts at pins 1 and 2 (relative to battery 0V). If you understand the schematic, a short circuit between pins 1 & 3 on that plug would be same as F18 switch being closed and your fan will run at 2nd speed.

[Trist28]

check the resistor pack and associated wiring

What and where is the resistor pack?

[S2central.net]

Front left corner down near the horns. Its maybe 15cm long and 3cm wide. It has three reasonably hefty connectors on it - do not mix them up if checking, cleaning etc.

[Mikes2]

It sits below the washer bottle attached to the chassis on an ABY. It's blue in colour about 4" long

[Trist28]

It sits below the washer bottle attached to the chassis on an ABY. It's blue in colour about 4" long

OK great - I know what you mean - For some reason I thought that was for the blowers in the car

[S2central.net]

If you pull relays 3 or 11 (in the main fusebox) it should help trace the fault down.
With both relays out and the fan still runs then you are looking at J135 or J155 misbehaving (or a wiring fault).