Rad Fans not working

MikeT · Post by **MikeT** » 07 May 2010, 19:50

Clogzz wrote:I’ve had to work out the cooling fan electrics about 5 years ago

My experience is from a few years later yet I've forgotten most of it already.

windysurferuk · Post by **windysurferuk** » 17 May 2010, 19:23

Finally got time to have another look at this.

I got at the bitron unit and remove the plug.If I short out pins 3 and 2 on the lefthand relay I get 12volts on pin one of the bitron, when I remove the wire from 3 and 2 there no voltage at pin one on the bitron.

Terminal 3 is free from corrosion.I can follow the wire from terminal 3 until it goes under the fuse holder in the engine tray and the wire is fine until here.

No idea what to do next!!

Clogzz · Post by **Clogzz** » 18 May 2010, 15:48

Hi Windy,

The voltage on terminal 3 comes from the fuse box, so that’s normal.
That part works, because you've had the fans spin up the thread.

Even with the key out, the 12 Volts from the 5 Amp fuse on relay terminal 1 must come through the relay coil to terminal 2, and also to Bitron terminal 1.

When the fans are not spinning, the Bitron lets the voltage come in from relay pin 2, and does nothing about it.
To run the fans, the Bitron shorts its pin 1 to earth, causing earthing of relay pin 2 to energise the coil and close the relay.

If there’s 12V on pin 1 of the relay, but nothing on pin 2, it means that the voltage isn’t coming through the relay coil from pin 1.
Since the relay is known to be good, it can only be making bad contact in the socket pins 1 or 2.
The relays can be swapped all around, providing that the lower one has a centre pin.

windysurferuk · Post by **windysurferuk** » 19 May 2010, 21:08

Thanks for the reply and all your help, but I've given up and bought a new car!!.

Not really anything to do with this problem but just fancied a change.

Pick up a Xsara 110 HDi , one owner form new 65000 mile next week

New car new problems

Clogzz · Post by **Clogzz** » 20 May 2010, 12:56

Hi Windy,

Congratulations for the new car, and best wishes with it.
We’ll soon have a new member enquiring about a Xantia with a fan fault.

windysurferuk · Post by **windysurferuk** » 22 May 2010, 11:56

due to having my motor home stolen I've cancelled the new car so now need to fix this

I'll get the multimeter out and have another go.

Is there a way to bypass the problem wires and just run new wires from the relays straight to the bitron?

Clogzz · Post by **Clogzz** » 22 May 2010, 15:58

Hi Windy,

Sorry to read about your motor home.

Tapping into the moulded Bitron plug is very fiddly, with great risk to wreck it.
Top right relay, pins left and right are the relay coil.
One has 12V from the 5A fuse, the other goes to Bitron pin 1, not sure which.

Try measuring from pin 1 of the Bitron plug to the relay coil socket pin that doesn’t have the 12V.
If it’s open, try removing the backing plate to reach behind the relay sockets to grab the thin wire going to the Bitron.
With a hat pin or something, pick into the wire and measure back to the socket terminal.
Keep picking your way to the Bitron until you find where the interruption is.
You can also pick from the Bitron end, but the wire will be difficult to identify from that end.
If you do find a good end coming out of the Bitron plug, you can plumb the socket terminal to it.

MikeT · Post by **MikeT** » 22 May 2010, 18:58

Clogzz, you have a pm, sir.

Clogzz · Post by **Clogzz** » 23 May 2010, 12:23

Your Lordship Michael,

Thank you for your PM, and it has been answered to your satisfaction.

Kind regards,

Terry.

_____________________________________________________________

pick from the Bitron end, but the wire will be difficult to identify from that end

Delayed reaction.
Not sure about the diesel car, but the petrol car with Bitron in the fuse box has a piece of 3-wire loom with plug and socket assembly dangling low in front of the battery.
They’re the wires from the Bitron to control the fans.
One wire is the low speed one where the fault is, another one is for high speed, and the 3rd one is earth.
The loom passes along the bottom front of the car, just the ideal place for rot and rust.

DickieG · Post by **DickieG** » 01 Jul 2010, 22:35

Earlier this week I discovered that my HDi is suffering from the same problem as Windysuferuk, namely both fans operate normally at slow speeds but only the N/S one operates at high speed (both fans operate at high speed with current applied directly so the motors are OK).

After a lengthy session of probing I've discovered that relay 1 (In the picture below) operates the slow fan speed by the Bitron unit earthing relay pin 2, in high speed only the other two relays are similarly earthed (pin 2), whereas according to the wiring diagram pin 2 on relay 1 should also be earthed when high speed is selected. Clearly the connection to relay 1 pin 2 works as it operates slow speed, but not fast

so from what I can deduce it appears that the Bitron unit may be faulty or am I going up the wrong path? Over the weekend I'll swap the Bitron unit over with a brand new one I have in stock to see if that makes a difference.

Clogzz · Post by **Clogzz** » 02 Jul 2010, 11:00

Hello Richard,

All 3 relays must be energised at high speed.
Relay 1 is energised when Bitron pin 1 is earthed.
Relays 2 and 3 are energised by earthing pin 10 of the Bitron.

If the middle relay is stuck in the low speed position, the offside fan won’t spin at high speed because it then gets supplied from the battery at both ends.

The Bitron is faulty if it releases relay 1 when it energises relays 2 and 3.
The relays can be swapped all around for as long as the middle one has a centre pin.
To test the middle relay, put it at top left of the triangle, as that will transfer the fault to the nearside fan.

I’ve had the top left relay sticking shut, causing the nearside fan to spin fast even with the car parked on a cold night.
A wallop on the relay fixed it for good.
You’ll sort that with your eyes shut and looking the other way.

DickieG · Post by **DickieG** » 03 Jul 2010, 18:47

After a day spent removing and refitting the front of my HDi I discovered that HDi's do not have a Bitron sensor, the fans are controlled by the engine ECU. Despite further probing testing and internet researching I'm coming to the conclusion that Xantia and Peugeot 406 HDi colling fans only run in unison when at slow speed, at high speed it appears that only one fan runs

bizarre I admit but every forum I've researched (loads) there are many questions asking why only one fan runs at high speed but no answers as to how to effect a repair.

If anyone has a HDi with both fans working at high speed could you please let me know.

CitroJim · Post by **CitroJim** » 03 Jul 2010, 20:39

DickieG wrote:I'm coming to the conclusion that Xantia and Peugeot 406 HDi colling fans only run in unison when at slow speed, at high speed it appears that only one fan runs

Now that's amazing....

Mind you, the HDi runs so cool it's likely all it needs but why only one

thorter · Post by **thorter** » 03 Jul 2010, 21:01

I'm coming to the conclusion that Xantia and Peugeot 406 HDi colling fans only run in unison when at slow speed, at high speed it appears that only one fan runs

No, thats not correct. Both run at either low or at high speed. If only one runs at high speed then there is a bad earth connection on pin 5 of the centre relay (or the relay itself is faulty).

Fred

DickieG · Post by **DickieG** » 04 Jul 2010, 01:00

thorter wrote:
I'm coming to the conclusion that Xantia and Peugeot 406 HDi colling fans only run in unison when at slow speed, at high speed it appears that only one fan runs
No, thats not correct. Both run at either low or at high speed. If only one runs at high speed then there is a bad earth connection on pin 5 of the centre relay (or the relay itself is faulty).

I thought that too but the reason that only one fan runs on high speed is that the engine ECU (that controls the fans on a HDI) only earths the centre and N/S relay pin no 2 it does not earth the O/S relay when in high speed although it does on slow to activate both fans in slow, I checked this by using a breakout harness fitted between the loom and ECU. All other pins check out correctly.

I've checked the loom right back from the relay's to the ECU with resistance checks and all is apparently well, I've swapped all the relays with spares, fed power directly to each fan, bridged contacts you name it I've tried it, I'm as confused by this as anyone else

I've only come to my conclusion in the absence of finding anything else I can check. The only other thing I can think of is the ECU isn't working correctly when it comes to switching on the O/S fan at high speed.

If someone has any further ideas I'll be very interested to hear them.