75ZT Community

Currently fitting a 2 wire 2 speed cooling fan in place of the inoperative 4 wire original on my 1999 Rover 75 Diesel.
This one is off a 2002 Diesel and it came with the later control box. I thought that it would then be a Plug & Play scenario, however, when fitted it would not function. I carried out all the standard tests and proved that the fan motor and the new Gold resistor is working by connection a 12 volt supply directly to the fan motor a) direct to get full speed and b) through the resistor to prove the low speed. I then started to check the car wiring and after a lot of testing I recorded the following voltages at the two fan plugs con the car wiring:- Large Black & Brown wires 12 volts and live all the time, with ignition on and off. Thin Yellow / Blue wire - 11.5 volts. Thin Blue and Red wire - 3.5 volts. Yellow /Grey wire - 0 volts ( direct to Trinary Switch ) The same voltages were also recorded through to the control box on the fan housing. The relays inside the fan control box were all individually checked and found to operate OK. Despite all the checking the fan will not operate when connected to the car wiring. Could the fault be with the small PC board inside the control box ? Anybody any Ideas ????? Jupiter

Can I just check. On the fan plug on the car, do you have 12v on the black as well as the brown?

Hi Duncan, My terminology error. Black wire is earthed to car chassis. I went out and double checked. Today I have extended the wires that run from the fan motor and the Gold resistor to the control box to allow me to reposition the control box in the engine compartment for easy access. The extended wires are 84 / 0.3 mm2 ( 42 amp rating ) Just refitting the Fan now. Had to use the classic today to go for cable. Jupiter

Hi Drumond.
Give this a try change the PCB (Printed Circuit Board) board from your old unit into the new uint and see if it works then if you have not doneso already, and get back to us Arctic.

PS is this the PCB board in the new control box of the fan you are fitting


And would you old one be the one below with the two brown wire ?


Take note of the wiring on the new two speed control box as below


as opposed to this three speed four wire version


There are also two type of PCB boards as below

Right, Thanks for that. I will do that tomorrow morning and advise accordingly. This had crossed my mind, however as the boards have different numbers, I ruled out changing them over.
Many thanks
Drummond

Jupiter wrote:Right, Thanks for that. I will do that tomorrow morning and advise accordingly. This had crossed my mind, however as the boards have different numbers, I ruled out changing them over.
Many thanks
Drummond

Drummond.
I went to a members late last year and he had the same problem he changed the gold resistor three times thinking it may habe been that the relays when i got there i asked have you checked the PCB ? his answer was no because he already had the two speed fan fitted as he was only changing the resistor, so no spare PCB i luckly had one we replaced it with the one i had from a three speed four wire and away it went and still going stroung now so worth a try Arctic

Artic, I changed the PCB boards over and the three speed 4 wire board is now controlling the Two speed fan. I can ONLY get FULL speed function. I carried out the Trinary Switch test but the fan only runs at full speed with full ventilation or Aircon on Auto. No slow speed , unless I bridge the relay. The car outside temperature is still showing minus 30 C even after connecting the bumper wiring up. So some progress but need to get the slow speed fault identified.
Drummond

Check the footnote on my drawing to concur with Arctics statement, some pcbs require the repositioning of the grey wire
when disconnected, the external temp will show minus 30 for a period of time, I this is still minus 30 after a couple of hours the ext sensor is either disconnected or has a fault

Hi Takestock, before I started the job of replacing the original 4 wire fan with the complete 2 speed x 2 wire + the relay box that came with it I checked it all out against your drawing and that is the circuitry I am currently operating on so thanks for this. Temperature gauge now up to + 23 C so working OK. Still cannot get low speed to work.
Drummond

using the on board diagnostics via the IPK (Instrument pack (IPK from the German)) at what temp does the fan come on to cool the engine?

Not sure how to check that ? If left on Econ setting Fan has not come on. Should I just leave it on tickover and see what happens ? ( see if it warns up )
Drummond

xpdfdocuments/Car_Interior/OBC_Diagnostics_Via_IPK.pdf

this is how to get into the diagnostics, when it is displaying the engine temp you need to know what temp the engine gets to to bring the fan on, ( you may struggle with the diesel as it is cold running) but you are looking for the fan to come on at 100 and stay on to 96 on the slow speed, if the fan doesn't come on to 106 then that is the higher speed. IF the fan comes on high speed at 100 then the red and grey wires need to be reversed in the control box

Eventually worked out how to access OBC (On Board Computer) and go through the sequences. Eventually got engine coolant temperature up to over 95 C and at 99C the cooling fan came on at HIGH SPEED. The temperature dropped to 95C in a matter of seconds. Could not get it any hotter. But definitely HIGH SPEED comes on at 99C. Will I do any damage to the PCB board by reversing the wires. ? Also do you mean the heavy Red and heavy Grey wires ? So in effect you are switching relays ? If so is the smaller relay then taking the heavier current ? I will start again in he morning if you confirm my points.
Cheers Drummond

Hi Drummond.
Now you have replaced the PCB board with your old three speed four wire one doe'sit look like this control box


IF so what you need is this and as above, Dave's (Stocktake) reference is to the thin grey wire and that is what you are looking for but you can wait for him to come on board to double check Arctic.

You are looking to have your control box like this, unless i am mistaken


Take note of the PCB boards tracks note the difference in the two with the grey wires and the date on the PCB board

Hi all, Firstly please let me thank all of you for your very helpful assistance is trying to locate this current issue. I really appreciate all the advice that has been given.
I refer to the last post from Artic and his two pictures. My current set up, which is only giving FULL SPEED on the cooling Fan, is as the picture dated 02/10/2011. The thin grey wire on my control box / PCB is cut off just as it comes out of the sealing grommet and this also seems to be the same as in this picture. I then checked back down the cable form towards plugs that connect to the car wiring and found the grey wire. It had been spliced into the thin Blue/Red wire about halfway along. Referring to picture dated 17/05/2013 the thin grey wire is crimped along with the Blue/red at the PCB connector. So in effect it forms the same circuit. So what is the function of the first spade connector ( from the date end ) ??? I will go out soon and log all the PCB dates and any other numbers I can find on the two boards.
Thanks for all the advice.
Drummond

WELL, I think I MAY have solved the problem. I swapped the THICK Red and Grey cables ( In effect changing the fan return feed from one relay to the other ) And Hey Presto !!! when I put the aircon on the fan ran at the low speed. I then carried out the Trinary switch test ( as outlined by Jules ). The low speed worked when the cables were disconnected from the switch and when I bridged the yellow and black wires the fan ran at full speed. So, in essence, it now appears to be functioning correctly. I will be testing it over the next few days and will update on progress.
Thanks again to everyone who offered assistance. It was most appreciated.... No doubt I will be back on the forum again. Now I can get some work done on the Jowetts !!!!!
Drummond

takestock wrote:http://www.75ztcommunity.co.uk/xpdfdocuments/Car_Interior/OBC_Diagnostics_Via_IPK.pdf

IF the fan comes on high speed at 100 then the red and grey wires need to be reversed in the control box

Sorry missed the continuing thread, that is the advice in the post above, sorry if it was not clear glad your sorted

Hi Takestock, initially I was not sure if that was what you were advising, however, once I gave it a bit of thought it did make sense. I was out in the car today on a reasonably long run and was trying to get the fans to come on without the Aircon. It was a reasonably hot day and I had the OBC set to 7. I could not get the coolant temperature to get above 88 C so no fans !!!!. But thanks again. Now MOT preparation time ........
Cheers Drummond

Well i got that mixed up good un proper i thought it was the thin wires

Just converted my diesel to a two wire aftermarket fan as per the above diagrams but when I turn the air con on the fan starts in low for a short while then goes to high even though the engine is cold, turn the air con off and the fan stops.
Tried the grey wire in both positions and makes no difference, unless I leave it disconnected then it stays in low?
Any ideas?