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Coolant radiator electric fan


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Hi, I've got a 2005 Superb with the BDG 2.5 TDI V6 engine and I have just had the air con re-pressurised and checked. All was okay except the guy mentioned that he thought that the electric radiator fan should be running at low speed all the time the air con is switched on, and it wasn't on my car. I have seen some posts which relate to this but can't definitively decide whether this low speed should always be on, when the air con is on.

 

I have looked at the circuit diagram from the service manual (page No. 67/7) and it seems that there are 3 relays which turn the fan on. The first is relay J279 (fan low speed, goes through a load resistor N39), switched on by the temperature switch F18 in the coolant bottom hose. The second is J280 (direct 12V to the fan for high speed), switched on by the second set of contacts in F18. The third is J397 which is a fan run-on relay which seems to be present only for the diesel engines, which feeds the fan through another load resistor N39.

 

Apart from the switch F18 the relays J279 and J280 have secondary actuation wires on the coil side which go somewhere off the circuit diagram to other areas on the car. One such connection goes to a point L9, which is listed as a connection -1- in the radiator fan wiring harness and I believe that this goes to the air con pressure switch F129, but the other goes to a point 55 (in a square box), which I can't find anywhere else in the circuit diagrams.

 

Does anyone know where this designation 55 can be found elsewhere in the circuit diagrams, which drives the fan at low speed?

 

The run-on relay J397 seems to be driven by A193 (in a circle) and J... (one of the engine control units). Does anyone know what triggers the run-on relay?

 

Thanks for your help, as soon as I understand the circuit and its' operation I shall start delving with the multimeter.

Edited by milespd
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The rectangular box numbers refer to the current track at which that wire continues. Current tracks are the numbers at the very bottom of each diagram.  When you get to the destination track, there'll be another rectangular box with the number of the current track you've just come from.

 

In the cars I've looked at, with a G65 refrigerant pressure sensor, the HVAC module watches this and triggers fan speed 1 if the G65 pressure exceeds 9 bar, speed 2 if it exceeds 16 bar, switch off speeds are 6.3 and 12 respectively ISTR. 

Not sure how an F129 works though.

 

Edit: This might be worth a read: http://nackuk.blogspot.co.uk/2013/02/that-dam-fan.html

Edited by Wino
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Yes the fan should run at low speed when the A/C is on.

 

Check that the fan works by connecting it directly to the battery.  Sometimes the brushes get stuck with carbon dust, so hitting the motor with a metal bar can free it off temporarily. Check to see if the fan connector gets voltage when the A/C is turned on.

 

The fuses for the fan are tucked away under the steering column, you need to remove the trim to access them. While you are there you could feel the relays to see if they click at the appropriate times.

 

A common failure is the power resistor, bolted to the main "chassis" frame beneath the nearside headlight.  It's a resistance clamped between two aluminium sheets.  There are three bolted cable connectors, unfortunately these are on the lower side (need to remove undertay to access).  Try shorting the connections.  You can unbolt the connections and then check the resistor for continuity.  The crimped connections may also need remaking if they are a mess of corroded copper.

 

That's a start.

Edited by Tdi1.9
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Thanks Wino and tdi1.9, your posts have been very helpful. I'll take a close look at the link, it looks useful. I'll post again when I have investigated more fully. thanks again, Paul

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  • 1 month later...

Hi, finally got round to investigating this. I disconnected the fan connector which sits in front of the power steering reservoir and measured the voltage. Came on when the aircon was switched on so assumed that everything was okay, except the fan itself. Bought new fan (VEMO) from Lott in Germany for about £85 including postage (how do they do it, nearest in UK from GSF was about £170?). Plugged the fan in, without fitting it, and it came on as soon as the aircom was turned on, off when aircon turned off so now I need to fit the fan. Anyone know if the old fan will come out without moving the lock-carrier? How about the wire routing, looks like it goes along the bottom of the aircon radiator. Advice much appreciated.

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Yes, the fan can be swapped without further dismantling, though it's a bit tight.

 

There is one small cross head screw that holds the fan, which can then can be rotated to release the bayonet tabs.  You can see how it works by looking at the new fan.

 

I ran the new cabling across the top of the plastic fan cowling and held it in place by drilling two small holes in the cowling and using a couple of  cable ties.

 

This avoided having to remove the plastic undertray, which looked to be necessary to access the original cable route at the botom of the radiator.

 

The fans often stop working because the brushes have either worn too short, or are stuck with caked on carbon dust.

 

An even cheaper fan option is to use one for the passat B5 (about £40 a couple of years ago).  It's the same fan, but the connector is different, so needs to be swapped for your original one. 

 

UKpassats has a "how to " here:   http://www.ukpassats.co.uk/phpbb/viewtopic.php?f=8&t=57919

 

about half way down the "engine" section.  You need to register to view, but it's free!

Edited by Tdi1.9
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Hi, finally got round to investigating this. I disconnected the fan connector which sits in front of the power steering reservoir and measured the voltage. Came on when the aircon was switched on so assumed that everything was okay, except the fan itself. Bought new fan (VEMO) from Lott in Germany for about £85 including postage (how do they do it, nearest in UK from GSF was about £170?). Plugged the fan in, without fitting it, and it came on as soon as the aircom was turned on, off when aircon turned off so now I need to fit the fan. Anyone know if the old fan will come out without moving the lock-carrier? How about the wire routing, looks like it goes along the bottom of the aircon radiator. Advice much appreciated.

 

...because no-one buys full price from GSF - they have a 45% off "discount" code every week it seems.  Ridiculous business strategy.

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