I have a 1990 XJS with A/C blower motor speed problems, I have three speeds my low speed is very very high the other two speed are ok. Has anyone had to deal with this problem. Thanks Lou

 

hmmm, we can wait and see if someone like doug knows, but I don't think the switch is a variable resistor, I believe there is one somewhere else and it is doing the switching for it.

Wouldn't want to tell you to pull the switch and find it doesn't do any of the resistance work

 

The blower speeds on your model are controlled by the climate control ECU and the circuit board inside each blower assembly. The circuit board has a transistor and a couple diodes...or some such. Nearby the circuit board is a relay

From memory the highest speed comes from the relay being energized. All lower speeds are controlled/commanded from the ECU by varying resistance to ground.

We have the Delanair Mk III diagnostic manual on the web site somewhere. If you're interested in doing your own testing I'll try to find it for you. You'll need a volt/ohm meter.



Cheers
DD

 

told you doug would have this one, hehe

 

Thanks Doug, is the ECU on the passenger side of the console and it looks like a baby grand piano? Lou

 

That's it !


Cheers
DD

 

Louis,

I suspect this is the usual and very common problem of the Darlington Transistor having failed. Is the speed high on both blowers (L&R) or just high on one side?

The Darlington Transistor is very well documented, you'll find lots of threads on many Jaguar Forums relating to this. Just spend 15 mins doing a search and read on the issue. If it is the problem, you can buy a compatible transistor from any good electronics store.

Good luck

Paul

 

Here's the Delanair Mk III training/diag guide

Cheers
DD

 

Thanks Doug

 

Thanks Paul

 

Paul, I just check it looks both sides are running at a high speed when it is on low speed.


Thanks Lou

 

Lou,

Very possibly both circuit boards / Darlington Transistors need replacing then.

Paul

 

Paul, Thanks Lou