Radiator fan low speed not working (resistor and relays are OK)

[Ondra_cz]

Hi,

I have a problem on my 2004 CDTI with low speed on radiator fan. At beginning I’ve noticed that A/C is not running continuously – the silver resistor was dead, so I have swapped it for golden one (with correct value 0.47ohm).

I have checked both speeds without engine running and it was ok, both relays are working. This was before the assembly. I have assembled everything with confidence that I solved it, but when I have tried the A/C with engine running, only high speed is working, but with significant delay. Then I have tried demist with the same result.

I have measured the resistor again thru the front grill and it is ok. Interesting is that when the high speed turn on during driving, the A/C is working fine without the outages like it was before, when the old resistor was dead. It seems to me that the high speed running continuously until I turn off the A/C.

Another finding – before this problem, when I turn off the engine with running A/C, the fan have been running at slow speed for a while. Now when the A/C is running at second speed, the fan stop working immediately I turn off the engine.

Is there a way how to check the signal for low speed? (from where the signal is coming?) I would appreciate any advise..

[T-Cut]

The Demist test is the standard method for checking the low speed. I suspect the resistor wiring/circuit. How did you connect up the wires?

Fan Testing: http://www.the75andztclub.co.uk/forum/showthread.php?t=35567

TC

[Ondra_cz]

Yes I have tried the demist test, but the fan turned on with delay on high speed, not immediately on low speed as it should do.

I test the both speeds by energizing the signal wires which are coming into the both relays, it was working fine.. So I suppose it might be a problem with the signal coming into the slow speed relay...

[T-Cut]

Yes I have tried the demist test, but the fan turned on with delay on high speed, not immediately on low speed as it should do.

If the low speed doesn't work, the aircon system overheats (when stationary) and trips on the high speed emergency cooling. This will puse on and off until aircon is turned off.


I test the both speeds by energizing the signal wires which are coming into the both relays, it was working fineThat sounds more complicated to fix since it involves the ECU.

TC

[Ondra_cz]

New finding - when I turn on the A/C with running engine, then as you said, the fan is turning on and off, but on low speed (small relay ticking on and off). The resistor temperature is really high I cannot even touch it (but this should be normal condition, right?). Could it be a faulty resistor again, even when I can measure 0.3-0.4 ohm on it?

[T-Cut]

- - - on low speed (small relay ticking on and off).

That's obviously the problem, but is it the relay or is it the activation signal? I think you should consider a T4 analysis.There's a good chance that the controller PCB has failed. It's a common cause of fan problems with the diesel models.

The resistor temperature is really high I cannot even touch it (but this should be normal condition, right?).

Yes that's normal. It's heating up whenever the slow speed relay closes.

Could it be a faulty resistor again, even when I can measure 0.3-0.4 ohm on it?

I don't think the resistor is the cause. You might contact French Mike who fixes/exchanges the PCBs

TC

[Ondra_cz]

PCB is not a problem because it is not there :-) I have 2 speed 2 wire fan with only two relays in the box, like on this picture below.

You are right, I will go to garage with T4..


http://i44.tinypic.com/15p4mee.jpg

[T-Cut]

PCB is not a problem because it is not there :-) I have 2 speed 2 wire fan with only two relays in the box, like on this picture below.

Oh, I thought it was a diesel.

TC

[Ondra_cz]

yes it is diesel - 2004 CDTI

[Union Wheels]

Hi Ondra_cz,
You appear to have the wrong fan fitted. Diesel fans all have a P.C board fitted to convert the signal from the engine management unit into voltage to drive the relays.

Pete.

[T-Cut]

Yep, it explains everything. The slow speed relay may be a little disorientated by the PWM signal from the ECU!;)

TC

[Ondra_cz]

Hi,
thank you for the info, I did not know that this is wrong version. When I disassembled the bumper, there was no visible reason to suspect that somebody modified it (connections, wiring, etc.)

Before the silver resistor died, everything was just right (demist, A/C - continuous low speed). The problem occured when I have changed the silver resistor for the golden one.. that is the only modification I have done...

[T-Cut]

I did not know that this is wrong version. - - - Before the silver resistor died, everything was just right (demist, A/C - continuous low speed). The problem occured when I have changed the silver resistor for the golden one.. that is the only modification I have done...

??? - It doesn't make sense. The diesel uses a pulse width modulated signal to trigger the motor relays and has a PCB to manage it all. So, a diesel fan system is different and must be replaced with a diesel type controller. If a 2-speed system from a petrol model is used, it won't work properly. It seems you've had a petrol control system fitted at some time. Whether it had a silver or a gold resistor, it couldn't work properly. Not as I understand it anyway. ??? But I'm sure someone will explain it.

TC

[stocktake]

Petrol relay box fitted to a diesel, seen it before, took me a while to realise first time but exact same symtoms. Get yourself the correct relay box wired in correctly and all should be fine.

[Arctic]

PCB is not a problem because it is not there :-) I have 2 speed 2 wire fan with only two relays in the box, like on this picture below.

You are right, I will go to garage with T4..


http://i44.tinypic.com/15p4mee.jpg

Petrol relay box fitted to a diesel, seen it before, took me a while to realise first time but exact same symtoms. Get yourself the correct relay box wired in correctly and all should be fine.


Hi Ondrej
You will need to make sure your control box looks like this below in the two pics