Just today on the way to work I turned the fan off because it was plenty warm in the car. It had been set at low. A little while later the car cooled off and I turned the fan back on. This time it will only run on one speed, which seems to be medium or high, regardless of where the switch is set. Doesn't matter if it is in auto or manual either. It stays at one speed. Only thing that changes it a little is switching to defrost. What has happened? I haven't been able to determine yet if it is both fans or only the driver side. Where do I go from here? This is a '91 Sovereign, 147K miles.

 

Muleears:
It is nothing more than an informed guess to say that it sounds like a resistor that controls fan speed has fritzed out. This same thing has happened on our Caravan several times. I can swap that part out in my sleep by now. On the Jag however, I don't know where it is or how it's done. Some folks have had problems with the fan/rotary switch itself; that tends to be a weak spot in these cars over the years.
How's that for a pool of ignorance?!
Scott

 

Muleears:
Sorry wasn't content with what I wrote so I did a bit more digging. This is from the JDHT service manual: "In the LOW, MED, and HIGH positions, information regarding the range of fan speed selected is received by the control module from the control switch... The fan speed is then electronically controlled by the ECM. So by selecting L, M, or H a level of speed in the range selected is received dependent on requirements."
Sounds to me like you need to replace the switch, which from what I've read elsewhere is both fairly easy and common.
Cheers! Scott

 

Thanks for all your research, you have done more work on this than I have today. That said, I just ran an errand in the car and it worked fine... I think I will keep an eye on that switch as you suggested.