Hi there,

my 1992 Daimler Double Six, fitted with the Delanair MKIII (final version), has been behaving strangely lately, and I’m hoping for some advice.

Under normal conditions, I drive with the climate control set to Automatic, the temperature at 75, and the fan on low. When I arrive at my destination and turn off the car, the blower fan suddenly starts running on low speed, but without any automatic regulation. Only cold air comes out of the vents. The fan does not switch off by itself and can only be stopped by moving the fan mode selector (Off–Low–Med–High–Defrost) to Off.
What’s particularly odd is that if I then turn the selector back to Low or any other setting while the car is still switched off, nothing happens at all.

In addition, the electric fan for the climate condenser runs continuously whenever the fan mode selector is not set to Off, even when the system is in manual mode and set to heating. This may be related to the fact that the climate system currently has no refrigerant, so the compressor does not engage, but I’m not sure whether this fully explains the behavior.

I would also like to ask whether anyone has documentation for the Delanair MKIII available as PDF files, such as workshop manuals or repair and troubleshooting guides.

Since there are many knowledgeable experts in this forum, I would greatly appreciate any advice or insight into why these two fans are behaving so strangely.
Thank you very much in advance.

 

This almost sounds like the usual failure of the Darlington transistor(s) at the blower motors. The typical failure, though, is that the blower fans simply continue running with the key "off". Your description doesn't exactly match.




Not sure about your specific model but many of the XJS V12 cars were configured this way. The aux fan operates whenever the compressor is engaged....and the compressor is engaged in all climate control modes, heating, cooling, and defrost


Somewhere in the archives is the Delanair III diagnostic manual. I'll try to find it

Cheers
DD

 

Go to this thread and scroll down to post #19 for the manual

https://www.jaguarforums.com/forum/x...-manual-83961/

The manual is for 1987 but will probably still be useful to you

Cheers
DD

 

Here's some good info on the blower motor/transistor problem

https://www.jag-lovers.org/xj-s/book/acblower.htm

Cheers
DD

 

This may help.

 

OK, thank you very much. I’ve done some research on these transistors, and it looks like this is indeed the faulty part. The only thing I haven’t been able to determine for sure is where exactly these transistors are located.

After reading the Jag-Lovers page, it seems that they are mounted inside the blower units for cooling purposes. However, I would like to confirm this before dismantling half of the car just to replace the transistor.

Additionally, I would like to ask whether there are any alternative transistors available that are more reliable and less prone to failure.

Thank you very much in advance, PS!

 

Yes the transistors are on the blower motor assemblies....which have to be removed to do the repair. Not a pleasant task I'm sorry to say.

Cheers
DD

 

OK, thank you very much, although this is not great news.

Is there any chance that the problem could be something other than the transistors? What I find particularly interesting is that both blowers show exactly the same behavior, and the electric fan for the climate condenser at the front also runs when the ignition is off and the climate/heating speed selector is set to Low. As soon as I switch it to Off and then back to any speed setting, it does not turn on again unless the ignition is switched back on.
Does anyone perhaps know of another possible cause for this behavior?

Thank you very much in advance.
-PS

 

Other possibilities are possible, yes. A schematic for your exact model would be helpful...but I don't have one. I'll do some mulling. Hopefully others will chime in.

Cheers
DD