Hi,

I have an XJ40 -90 there the entire ventilation system seems to be dead.
In addition to this, the heating are on full throttle......
I can, when turning the fan control from "off" to low speed, here that a relay or something is activated someware in the dashboard.
Except from that the entire control unit seems dead apart from the lights.....
When the problem started, it worked fine from time to time but now it is dead.
All fuses are ok.

Any ideas? Control unit blown?

Cheers,
Conny

 

My guess would be the microswitch on the back of the control unit, I think it's a known fault on the earlier '40's. Take a look at the "blowers not working" thread in this forum for instructions on repair.

Late model 40's suffer from cracked solder joints in the footwell fuseboxes.

good luck

 

Thanks,
It was the micro switch....
However, the heating is still on full throttle so I have more work to do....
Any ideas?

 

Karlsund,

You should read the following post: (it's specific to your model year and the presence of cabin heat issue)

http://forums.jag-lovers.org/av.php?1543069n20

On earlier models a person would inspect the heater control valve located in the engine bay, very close to the firewall. There should be a short piece of hose from the firewall to the valve, then a hose from the valve to the block. Also, a red vacuum hose connected to the top of the valve.

The valves fail and allow constant water flow from the block through the cabin heater core, thus you always feel heat on the interior.

Many people have eliminated the valve and instead installed a ball valve and manually open/close it depending on the season. Folks in southern hemispheres rarely need to heat the cabin, thus they put the ball valve in a closed position and usually leave it there.

Other climates where there is a wider variety of change, you simply need to remember to open the ball valve in the fall or late fall for the colder months, then close again in the spring.

I have replaced my heater control valve and when it acts up again, I will install the ball valve.