is bthere a linkage that l can check?car is 02 model with a/c

If you are talking electronicly heated front window? the answer is its suppose to do that!!
As on all cars with this the drivers side clears last to ensure you are driving safely with all your windows clear!
sometimes it needs a second press of the button.

If you are referring to the hot air demister, check if there is anything trapped in the air vent. Maybe using a mirror will be more visible.

It is an electrical problem that needs an electrician i`m sorry to say.When the Laguna is at an age of your car,seems to start having problems My son had an 02 Laguna that seemed to be wanting some thing fixied every month,the spares are very very expensive,in the end he got shot of it,sorry.

Check your coolant level, if screen is getting misty and damp, the heater matrix may be weeping , not uncommon !