We have two doors. The front one has a gas strut to hold it open at 90 degrees, otherwise it would hit the awning support.
The rear door opens all the way out (amost 180 degrees) and has one of these style catches:
There's a third kind I've heard of but no direct experience with - a friction hinge. It basically just stays where you leave it, more or less.
Looking at the external pictures on Jayco's site, your door situation is much like our main door in that it can't open more than 90 degrees without hitting the awning. So based on that and your description, it sounds like you're missing the gas strut that snaps on the two mounting posts. In theory, you *should* be able to open the door to 90 degrees and measure the distance between the posts to determine the size strut you need. I've never needed to replace one before, so I could be completely wrong as well. One dealer near me stocks a bunch of different sizes, perhaps your nearby dealers do as well.