Rad Fans not working

This is the Forum for all your Citroen Technical Questions, Problems or Advice.

Moderator: RichardW

thorter
Posts: 106
Joined: 22 Feb 2005, 03:07
x 2

Post by thorter » 04 Jul 2010, 10:55

Well now! I am fairly sure the HDI is supposed to operate like previous Xantias, ie both fans in series (low speed) or both parallel (high speed). I think mine (HDI 110) does, but it is difficult to check in a temperate climate (currently 13C here, and rain), unless by fooling the ECU.

Unfortunately, the coolant temperature is measured by a NTC thermistor connected to the ECU, not the previous simple thermostats. Details are given in the Revue Technique for the Xantia, but unfortunately look a bit suspect. The table of resistances stops at 80C, surely wrong.

For what its worth, here are the top 4 values (between pins 1 and 2 – 3 is warning light);
40C – 2600 to 2710 ohms
50C – 1770 to1830 ohms
60C – 1220 to 1270 ohms
80C – 620 to 636 ohms
I suspect the wrong table has been copied in. It might in fact be swapped with the fuel temperature table, top 4 values as follows.
60C – 557 ohms
80C – 273 ohms
100C – 143 ohms
120C – 80 ohms

Anyway, you could try substituting a 1K potentiometer if you are handy with electrics, and adjust though the travel to simulate the range of temperatures. I doubt it would do any harm, but perhaps avoid zero ohms (eg put 47 ohms in series). If you are lucky, the ECU should output the corresponding fan commands (and if not you will have a fault light due to incompatible values!).

Let us know how you get on, it may be very useful information.

Fred

User avatar
Clogzz
Posts: 2072
Joined: 15 May 2005, 18:04
x 15

Post by Clogzz » 04 Jul 2010, 11:48

:?

If there’s no high speed for both fans, then there’s no need for three relays at the front.
One fast fan at one end isn’t as good as two slow ones blowing through the whole cooling surface, least of all as emergency cooling for the air conditioning condenser.

User avatar
DickieG
Monaco's youngest playboy
Posts: 4897
Joined: 25 Nov 2006, 10:15
x 12

Post by DickieG » 04 Jul 2010, 11:54

Hi Fred,

Thanks for your reply, the way I've been testing the fans speed is by using an actuator test with my Lexia, if its confirmed that both fans on a HDi should run at high speed together I'm tempted to work around the "problem" by way of using a fourth relay :roll:

User avatar
DickieG
Monaco's youngest playboy
Posts: 4897
Joined: 25 Nov 2006, 10:15
x 12

Post by DickieG » 04 Jul 2010, 12:05

Clogzz wrote::?

If there’s no high speed for both fans, then there’s no need for three relays at the front.
One fast fan at one end isn’t as good as two slow ones blowing through the whole cooling surface, least of all as emergency cooling for the air conditioning condenser.
That's what I think, what I can't work out is why the ECU doesn't send a signal/earth to trigger the O/S fan, I know that the same connection works as its the same contact that turns on the fans at slow speed, confused? Yes I am!

The engine ECU doesn't have any faults recorded (its that ECU which is used via Lexia for actuator tests) the only question mark I have lingering in the background is that the A/C ECU regularly has a recorded fault of "Recirculatory motor fan speed irregular" or similar. As fas as the A/C goes I've replaced the heater fan and ECU but that fault still appears whenever I carry out a fault code reading. According to the Citroën diagnostic manuals the radiator fans are controlled by the engine ECU and not the A/C, I've carried all the tests listed in the manual and all are correct :?

User avatar
Clogzz
Posts: 2072
Joined: 15 May 2005, 18:04
x 15

Post by Clogzz » 04 Jul 2010, 12:32

Looks like the HDi’s aircon pressure sensor then goes to the engine ECU for lack of a Bitron.
If the ECU’s high speed output can be trusted to feed three relays at the same time, you may plumb a diode from there to its relay 1 output to restart it … quicker than plumbing in a fourth relay.

:?

Image
Last edited by Clogzz on 04 Jul 2010, 14:18, edited 1 time in total.

thorter
Posts: 106
Joined: 22 Feb 2005, 03:07
x 2

Post by thorter » 04 Jul 2010, 14:17

Thanks for your reply, the way I've been testing the fans speed is by using an actuator test with my Lexia, if its confirmed that both fans on a HDi should run at high speed together I'm tempted to work around the "problem" by way of using a fourth relay
Perhaps the Lexia only sets or clears the discrete output for each relay separately. That would make sense for diagnostics. So the fans may well work in tandem in the real situation that the water temperature is over 107C or whatever.

You should be able to simulate that by the method I suggested, assuming you have the bits to do it. It should in fact be quite safe, since the ECU software can be expected to cover survival in fault situations, eg when the water pump has failed.

Fred

User avatar
DickieG
Monaco's youngest playboy
Posts: 4897
Joined: 25 Nov 2006, 10:15
x 12

Post by DickieG » 04 Jul 2010, 18:28

The mystery is now solved :D
thorter wrote:
Thanks for your reply, the way I've been testing the fans speed is by using an actuator test with my Lexia, if its confirmed that both fans on a HDi should run at high speed together I'm tempted to work around the "problem" by way of using a fourth relay
Perhaps the Lexia only sets or clears the discrete output for each relay separately. That would make sense for diagnostics. So the fans may well work in tandem in the real situation that the water temperature is over 107C or whatever.

Fred
You were right there Fred, well done :D instead of using my Lexia to trigger the fans at high speed I removed the blue connector form the sensor on the thermostat housing and both fans operated at high speed together :lol: so after a weekend of dismantling the car and head scratching it was working correctly all the time :roll: Doh!

Thanks for your help and suggestions chaps, I've now learned something extra about Lexia actuations :evil:

RichardW
Forum Treasurer
Posts: 8656
Joined: 07 Aug 2002, 17:12
x 285

Post by RichardW » 04 Jul 2010, 19:42

So can you test the other fan with the Lexia...?

I managed to get the fans on high on my HDi once - couple of years ago, sat in a traffic jam on a hot day at 30°C (yes, even in Scotland some times!) SWMBO didn't want the A/C on. When we got to melting point she gave in and I put it on. Water temp was around 100°C at the time. A minute or so later, there was a huge roar and the fan(s) were on high - I can't say for sure both were running, but there was a huge roar, and the whole car was vibrating, so I rather think both were running :lol: