I live in a modular with no way to get to the attic/crawl space. My ceiling has cracked down the seam. Need advice on how to fix

Debbie, is the ceiling sheetrock or other?

Sheetrock tape and tapeing compound.

Good luck

Chuck

Does it have Texture?
Decorative Beam or molding?
If you have the Money, and don't want molding, Whole ceiling may be the way to go.
If you know of someone who can patch with no evidence, would be good and may be hard to find.

The ceiling is sheetrock with a popcorn texture over it. After I scrape it how will the tape hold it up?

I'v seen people use spray bottle to apply water on popcorn to allow easier scraping.
Might consider a Knockdown finish, do any lighting changes prior to final finish.
The tape covers the screws. You should be able to scrape carefully and leave the tape intact.

Since there is are no studs close to the crack to screw the ceiling too, the nearest stud is about 6 inches, will the atpe hold?

Try paper drywall tape and put drywall mud behind the tape wipe it smooth apply a coat of drywall mud over the tape after the first coat drys sand the edges and apply the popcorn texture with a hopper gun

This may sound dumb but, how do I hold the seam together (even) while the mud is drying? The seam is separated the entire width of the home, with one side of the split hanging lower than the other, and is not located near a stud so I cannot use screws.

Remove s/r to the ceiling beam on each side.
Nail 2x4 on each beam even with bottom of beam.

Screw new s/r on 2x4's. Tape and compound.

Good luck

Chuck