[V8] Door lock de-icing system not functioning.

[Gunter Lorberg]

Anyone have any experience with the door lock de-icing system?
 
After some prolonged wet and above freezing weather, things quickly cooled down and I could no longer turn the door cylinder locks open without repeatedly heating up the key with a barcecue lighter to warm things up.  This was despite the use of gobs of lock de-icing fluid AND pulling up on the door handles for > 30 seconds to activate the heater as per the owner's manual.
 
Does anyone know of a quick way to check the functioning of this system?
 
Thanks.
 
Gunter
Toronto
(2) 1990 Canadian V8's with slushbox trannies