...84 XJ6..any ideas?

 

The only time I got foggy windows with the heat on was when the heater core sprung a leak. NOT in a Jag!

I Really hope that's not your problem, because mine was not easy even though the core was relatively accessible.
(';')

 

Thanks, that's what I thought, but I don't see any coolant escaping...

Second choice?

 

Dampness in the cabin from any source will do it. Damp rugs, rainwater leak.

The climate control system ....if working properly...will dehumidify the air to prevent fogging

Cheers
DD

 

connect the a/c compressor!! it is supposed to run with the heater.

 

Is it possible that your recirc flaps are stuck closed...or held closed. Recirculating heated air in a car during winter often can cause windows to fog. Just a thought.

Cheers