Passat Fan fix - with your help ?

[Col]

The purpose of this thread is to hopefully work through a fix for the incorrectly functioning aux cooling fan on my B5.5 Passat. As you no doubt know the Passat has a mechanically engine driven fan with a viscose coupling AND an electric auxillary fan. This fix with your help, hopefully will sort out my problem and serve to help others.

Also see my other thread;
https://www.vwaudiforum.co.uk/forum/s...ad.php?t=42809

It is a 2002 PD(130) TDI UK car, engine code AWX with climatronic.

First i'll explain the normal operation of the fan and how it is connected;

1, The fan is a basic single speed fan controlled by both a two stage thermal switch mounted on the radiator and a signal generated by the ECU. All three circuits are controlled via separate relays. The relays share a common 40amp fuse (on my TDI but maybe either 40, 50 or 60amp depending on the car). The switching side of the high and low speed relays are share a common 5amp fuse. Both the 40amp and the 5amp fuses are located on the relay holder up above the pedals. You need to remove the trim panel above the pedals to access them.

2, See my crude wiring diagram for how it is all connected.



3, Operation;

Engine on, aircon / clima OFF, the fan operates via the thermo switch on the radiator, low then high speeds.

Engine on, aircon / clima ON, the fan should be on all the time on low speed (I assume switched via the ECU relay). The radiator thermo switch will still control the high speed.

Also and although I've not shown it, there is another connection on both the low and high speed relays (switching side) which I cannot identify from the wiring diagram where they go but would assume they also go back to the ECU as my fan pulses at high speed although the coolant would not be hot enough when I've been testing it (see below for my problem).

The problem with my car;

Sat in really bad traffic the other evening my aircon started hissingand cut out. Traffic cleared and it started again. Upon investigation, the aux fan was not working at all. Numerous tests later and I established that the fan was itself dead so I changed it (£159.00 ouch) also whilst doing that I noticed my radiator was showing the classic signs that Passats do, of a leak where the header tanks join the cooling matrix. Changed that, another £70, ouch!

Anyway, now the fan works, it still doesn't!

It will pulse on high speed for about 60 seconds then stop for about 2-3 minutes then pulse on again for 60 seconds. Having researched this, and my fan has never worked it turns out since I've had the car which I bought 2nd hand, the fan should operate at low speed all the time the climate control / aircon is on. It doesn't.

Much more research and testing has led to conclude that the resistor pack is knackered. VW (bless them) want £90 for a new one !

Piccy below showing di-sected fan resistor pack, note the water ingress;



Piccy below intact resistor pack, it is normally located on the underside of the passenger side chassis leg right up front;



What I intend to do is use 3rd party resistors to provide the low speed function, I'm looking at Arcol or similar items, like this;



My questions and help required by anyone who knows their electrics is / are;

How to correctly size the resistors?

Possibly measure the current drawn by a functional fan system to aide in sizing the resistors? Could someone measure the amps drawn by their working motor on low speed?

Any help of advise much appreciated on the sizing of the resistors?

To help, the fan is rated at 300 watts.

The intended loaction where I'm going to mount the resistors would be under the coolant expansion vessel on a heatsink plate, assume ambient temperature to be that of the engine compartment. If this limits what I can do, I'll consider mounting the resistors back under the chassis leg where it would be cooler.

Here is how I propose to wire it;



You may think I'm mad but spending say £10 on a couple of chunky resistors is better than spending £90 on something that will no doubt fail again !

[a8 tech]

geek
go for it

[Col]

geek
go for it

Cheers Big-Ears but I was expecting you to tell me what size (ohms & watts) resistor I need ?

[a8 tech]

http://www.sengpielaudio.com/calculator-ohmslaw.htm
http://www.servicematters.com/calc/calculate_watts.htm
http://www.sengpielaudio.com/calculator-ohm.htm
Dont forget both the resistors will be equal .


Voltage or volt E or V = 12 volts V
Amperage or current I = 25 amperes, amps A
Resistivity or resistance R = 0.48 ohms Ω
Wattage or power P = 300 watts W

at your own risk,i would check the actual current draw

[Col]

http://www.sengpielaudio.com/calculator-ohmslaw.htm
http://www.servicematters.com/calc/calculate_watts.htm
http://www.sengpielaudio.com/calculator-ohm.htm
Dont forget both the resistors will be equal .


Voltage or volt E or V = 12 volts V
Amperage or current I = 25 amperes, amps A
Resistivity or resistance R = 0.48 ohms Ω
Wattage or power P = 300 watts W

at your own risk,i would check the actual current draw

Cheers!

The 300w at 13.4volts = 0.59 ohms then.

So by my crude reckoning, I'll try a 1 ohm resistor.

[a8 tech]

Should be fine.But dont blame me if you have a thermal incident

[Col]

Should be fine.But dont blame me if you have a thermal incident

That is what fuses are for !

[Col]

Update.

I bit the bullet and bought a new stock resistor pack from VAGPARTS for a very reasonable price compared to the dealer.

Bit of a chore to fit as the lock carrier has to go into the service position to gain access to the damned thing.

All back together now and the fan works exactly as it should i.e. slow constant speed all the time with the aircon on.

As the old one suffered from water ingress which destroyed it, I applied some silicon along the joints where the two halves fit together. Hopefully this will now be ok for another 140k !

Dear old do this has been, new fan, new radiator and new resistor pack, but at least I know my cooling system is now spot on.

Pic below, front of new resistor pack.



Pic below, rear of resitor pack, you might just see the silicon I've applied to the edges.