Air con fan sensor

Hi guys. The clue is in the question...Is there one? I got the air con regassed today by a bloke who appeared to have the right kit. A plug in and play unit that can be programed to a specific vehicle.. All good.
Driving back home I have an outside temp of 20o. So I set the air con for 20o, auto function, recerc selected. As I go along I have got my hand over the vents behind the front seats. After a while the ice cold air changes to slightly warm, then after a while cold again, and so on. All good as I guess its senseing that the interior has reached the selected te
mp, and is coming on and off to maintain that temp.
However when its reached it preselected temp the fan keeps running at max speed. I was expecting it to slow or stop until it needed to cool the interior again.( My mates BMW will). So is there a sensor that should slow the fan or is this normal?

s long as it keeps the 20*C by controlling the temperature of air the sensor it's ok imo...as a matter of fact the interior temp sensor is near the mirror and headlamp adjustments buttons, it has a grille in front of it cos it's equipped with a small fan, you can reach it by opening the cover under the steering wheel...but for the time leave it alone, if the fan works only on max speed and you can't reduce it's spin with the manual controll your problem is this:

http://www.landyzone.co.uk/lz/1502260-post15.html untill then by exeprience i can tell you to use only the Toshiba transistor cos the other alternatives dont last or dont work properly

Hi S/F.
Thanks for the reply. I have read the links you posted and have been out and checked the functions. When on Auto it runs at full speed and never slows down, drove 200 Ks and nothing changed.
However I can lower the speed manualy in 5 steps from little blow to the high it constantly runs on.
From my understaning of your threads it the transister ? next to the blower motor under the glove box thats at fault.
Is this correct or should I read the threads again ?

if you can modify the speed with the manual controll the transistor is ok, if it's blown you have full blower no matter what you do... what if you set higher or lower temperature from the buttons when it's on auto mode? still no change in the blower speed?... e.g. measure the temperature within the cabin with a thermometer and set the aircon temp to that temp...the blower must slow down then...if not i'm affraid there's some trouble with the management...i'll check the diagrams and come back to you if i find something suspect for this issue, might be the sensor as you firstly thought... eventually unplug the sensor and see what happens

OK. I will wait for the sun to come up and test.Thank you.

Hi S/F
Tried the temp check. Going from lowest temp setting to a high as it will go, the temp inside the vehicle changes as you request. The blower stays on max all the time no matter what the inside temp. You can slow it manualy but even then it stays at the speed you set it at no matter what the inside temp.

Strange issue, i'm on it and thinking, first of all run a diagnostic on it to rule out the sensors cos from what you say it seems an ECU missbehaviour, that's why:

RAVE said:

Blower control
The ATC ECU operates a blower relay, power transistor and power relay to run the blower at one of 31 stepped
speeds. All speed steps are available in the automatic modes of blower control. In the manual mode, speed steps 3,
10, 16, 22 and 31 are used to provide slow, three intermediate and fast blower speeds. The ATC ECU energises the
blower relay and modulates the power transistor to operate the blower for speed steps 1 to 30. For speed step 31, the
ATC ECU energises the power relay, which switches the earth side of the blower motor direct to earth, bypassing the
power transistor.
In the automatic, economy and defrost modes, blower speed is corrected for vehicle speed to compensate for the
increase in ram effect on the inlet air as the vehicle speed increases. Correction begins at approximately 50 km/h,
when blower speed is progressively decreased as vehicle speed increases, until a maximum decrease of 13 steps
occurs at 123 km/h. Similarly, blower speed increases as vehicle speed decreases down to approximately 50 km/h.

Click to expand...

.here is the diagnostic procedure(unfortunately it doesnt cover the ECU:


this ECU is very easy to remove can't you borrow a known good one from somebody to make a test, it's plug and play

sierrafery said:

Strange issue, i'm on it and thinking, first of all run a diagnostic on it to rule out the sensors cos from what you say it seems an ECU missbehaviour, that's why:

.here is the diagnostic procedure(unfortunately it doesnt cover the ECU:

this ECU is very easy to remove can't you borrow a known good one from somebody to make a test, it's plug and play

Click to expand...

Dianostic check shows 00..No fault found. There is no chance of another ECU, mine is the only one in the area. I am reading on your post that the fan speed should increase/ decrease with the road speed. Mine has never done that.
There is a guy some distance away who claims he has " dealer standard diagnostics". and is a internationaly recognised auto electrician ([email protected]).
If he is telling the truth, do you think he would be capable of fixing it? or is a main dealer job. TBH he is close to the main dealer, and if he is as good as he says he is I would expect them to sub it to him anyway. Landrover Malaga are more interested in selling RRs for cash to fat rich men with dubious incomes than a secondhand Disco with a dodgy aircon.

Avoid main dealers imo, they will start to replace randomly the involved parts with new genuine ones then they'll rip you off... a good auto electrician would sort you out or give you the verdict that the ECU is fubar'd, your problem is that the ECU doesnt send signal to the transistor when it's on AUTO mode, it works only on manual command which rules out the transistor, the ECU gives feed permanently on the UR wire to the power relay which gives earth to the blower keeping it on full speed(31), that's it's only purpose... try to remove the power relay...then if the ECU is not totaly failed you must get all the other speeds(1 to 30) except the maximum cos the blower will get the earth path managed by the transistor, i put you the relevant part of the scheme, if you dont have it download a RAVE and you'll find all the connectors and pin disposals in Electrical Llibrary-Connector views, a good electrician with all these info's must be able to get to the end of it, if you can't or feel that it's hard for you send me an email adress and i'll attach you all the relevant points where measurements must be made.




the relay is behind the glovebox

ECU lost its' earth?

Hi S/f. Thanks for the offer of the onfo. My e mail is [email protected]. I will pass this to the auto electrician and let you know how I get on.
I am hoping he will think to also check the earth as suggested by David.