hey guys as i was driving today my rear windshield got very fogged and i turned on the front and rear defrost to clear it up

my front and sides got clear immediately but not the rear..
now i left it on for awhile and nothing, all that happened was that it got more fogged up. i parked the car and when i was driving back home turned it back on again and nothing still.
anybody know how i can check if maybe a cable is unplugged or something ?

 

I am having the same problem. The light on the dash comes on, the mirrors on the outside clear up but the rear window does not defrost. I checked the connections behind the passenger side C Piller molding and they are attached. The car has never had tint and the defroster strips are in excellent shape. I understand there is a relay somewhere but I cannot find it. If anyone can help I would appreciate it.