When the fan is in the off position, the fan will blast on high for just a second, then cut off, and a few seconds later, it will blast again for a second. This repeats every few seconds. Any idea what might be causing this? Has anyone else experienced this?

Thanks. Km

 

Are you allowing the car to warm up?
The heater system incorporates a temp sensor and fan will not run continuously until a certain water temp is reached.

 

I only just now noticed you say fan switch is OFF, in that case l quess a faulty fan switch may be the culprit.

 

If you are referring to the interior hvac fan(s), then are the drivers and the passenger side fans both exhibiting the same symptom?
Each side has their own blower fan and each has their own voltage regulator for
the fan speed control.
If both fans are exhibiting the symptom then the fan speed selector switch may have a problem. If only one of the blowers is showing the symptom, then you have a blower control circuit problem.
The blower speed control circuits are inside the blower assemblies.
There are a couple of threads on how to repair the units if you have any electronics repair skills.
This is a link I used for repairing the control module:
http://www.jag-lovers.org/xj-s/book/acblower.htm

The newer models of the XJS (95-96) use an entirely different control circuit.

Or you can order refurbished units from CoventryWest.

The hard part in repairing these units is removing them from under the dash.
I found that removing the seats worked wonders in the blower removal process.

P O R - Press On Regardless

 

Km,

I thought that the pulsing when off problem was symptomatic of the typical Darlinton transistor failure.

I've got it on my car at the moment, coupled with one of the fans running at speed 2 when set to speed 1. Both problems appeared at the same time and I'm certain it will just be the Darlington transistor.

Good luck

Paul

 

I recall that the most typical failure mode is that the fan simply stays running, even with the engine off and key off. The 'pulsing' part sounds like a different twist to me.

Or not. It's been years since I had to deal with the problem so I'm a little foggy.

There's also a diode and a relay in each blower assembly as well, as I recall, that might be worth thinking about.


Cheers
DD