98 Winstar no heat in ceiling vents

I was wondering if anyone would know why I cannot get any heat out of my rear ceiling vents in my 98 Windstar. The AC runs through it, but I cant get any heat. Any feedback would be appreciated. Thanks.

Heat doesn't come out the ceiling vents, they are only for A/C. Heat comes out the floor vents.

i had a gut feeling that may be why. I just wasnt sure though. Thanks.