Fan Speed

jthorne · Postby **jthorne** » Fri Jan 04, 2008 7:36 pm

Hi,

My air con works brilliantly however in my previous XJS once the temperature set had been reached the fans would go onto a kind of "tickover" setting and would be almost inaudible, in this car ('93 6ltr Conv) the fans stay "up" at all times, is it possible to stop this or am i being too picky?

Cheers

Jon

ptjs1 · Postby **ptjs1** » Sun Jan 06, 2008 3:40 pm

Jon,

I think that your car has the very late XJS climate control system. In which case, the variable fan speed only works when the 2nd fan speed is selected and the system is set to run in Auto mode.

I don't if that helps at all, but it may explain why the fans are running at preset speeds.

Paul

jthorne · Postby **jthorne** » Sun Jan 06, 2008 6:34 pm

I didn't know that! Thank you, i'll give it a go tomorrow and report back....

jthorne · Postby **jthorne** » Mon Jan 07, 2008 11:13 pm

Looked at the book and it says for my car the fan speed should be variable for both the low and medium fan settings. Took it out for a short while today and could not tell and great difference but will have a longer drive later in the week and let you know.....

ptjs1 · Postby **ptjs1** » Mon Jan 07, 2008 11:20 pm

Jon,

Technically the 1st speed is a variable speed setting, but you'll struggle to hear the difference. If you want to test it, put it in Pos 2, switch on the aircon and set the temp to a setiing which seems as if it roughly matches the temp of the car and set the face level vent control to the hot side. If the system is working properly, you will definitely hear the fan speed dropping as the car reaches the set temp.

Good luck

Paul

jthorne · Postby **jthorne** » Wed Jan 09, 2008 5:31 pm

Ok so long run today (London-Oxford-London -190mls) and the fan does not alter speed at any temperature. It's not the thing under the dash near the passenger side fuses as i disconnected that and the temp just kept getting hotter and hotter. So my next question is on a facelift car where are the other sensors? I assume its a delanair mkIII....

ptjs1 · Postby **ptjs1** » Wed Jan 09, 2008 6:38 pm

Jon,

Sorry, I've realised that you haven't got the very late system with the revised controls in your car. You should have one the last of the R12 systems. I can send you a wiring diagram if that would help you. Just drop me an email.

I know there are others on here with more knowledge than I have of the aircon systems (Mark B, AlMcl, Pop Rivet etc) who I'm sure can help better than I can. However, for what it's worth, it seems that the in-cabin sensor is working correctly as, when you disconnect it, its stops the temperature control. I believe that it is the signal from this sensor to the aircon ecu which also initiates the fan speed dropping. Therefore, my limited knowledge would say that either the signal from the ecu to change the fan speed is not working, or more likely, the rheostat (or similar?) controlled circuit in the fan blowers is not working.

That's about as far as I can go! Let me know if you need the wiring diagram.

Paul

almcl · Postby **almcl** » Thu Jan 10, 2008 8:02 pm

Jon

The speed control for each fan is achieved by means of a transistor mounted on a board inside each fan case. If both fans remain on the same speed throughout a journey, (in auto and both knobs horizontal)either the same (quite unusual) fault has occurred on both or they are not getting the slow down signal from the air con ecu.

Worth looking at the ecu (behind the RHS cheek panel) if water etc has run down the side of the blower there may be some corrosion tracks affecting things.

jthorne · Postby **jthorne** » Thu Jan 10, 2008 9:26 pm

Hi thanks for this, I' m sorry but right hand cheek panel? I don't know where this is!

almcl · Postby **almcl** » Fri Jan 11, 2008 2:18 pm

but right hand cheek panel? I don't know where this is

My apologies, it's the panel that the footewell vent on the centre console is attached to, by the UK driver's left knee. Undo the two cross head screws and slide the panel forward about a cm to disenage the lugs. Then look upwards on the side of the side of the climate control unit for an item with a multiplug attaching. Any corrosion here might be cause for concern.

poprivet · Postby **poprivet** » Fri Jan 11, 2008 4:33 pm

There is also lots of information on the blower motor problem already discussed in other topics in the 'Air Con' section.
Pop

Mark_B · Postby **Mark_B** » Mon Jan 14, 2008 2:02 am

Hi If this is the D Mk3 I'm familiar with, there's a good test that can be done without taking anything to bits. It's similar to the test Paul suggests, but this one eliminates the effect of the temperature control function by setting temperature to manual.

Pull outwards the left temperature knob <click>, to select manual, set it to centre-travel. Set right knob to Low or Norm. The fans should now drop to minimum speed, irrespective of the in-car temperature. On Low setting, they are almost stopped. The fans pick up when the left knob turned in either direction.

One or both fans might be racing. If so, in my experience it's usually the blower unit, not the ECU.

jthorne · Postby **jthorne** » Sun Jan 20, 2008 5:05 pm

Ok, so after extensive testing this weekend it seems that the passenger side works perfectly and the drivers side will not alter down to it's lowest setting even in manual mode (thats a speed lower than normal "Low").

Ideas? I have looked at the wiring and all looks to be fine.....

Mark_B · Postby **Mark_B** » Mon Jan 21, 2008 6:18 am

By the sound of that symptom, the blower unit itself. I betcha it's the 4148 diode dissolved away on the triangle shaped circuit board, part of unit. It's nearly always that. Have to remove blower to get to it.

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