'1978 30 foot Dodge Swinger

For the manual I would try a Google search. You never know someone may have put it online.

What engine?
The AC could have frozen bearings from lack of use. Try to start it on fan mode before turning compressor.
Pictures?

a 78 model will have either a 360 or 440 cu inch engine on a Dodge 'M" series chassis

that bodge swinger with AC confederation might have a 413 also

i had the 413 'wedge head' semi-hemi
in a 1972 Lifetime Premiere,
it was phased out of the truck chassis line before 78

440 parts are easier to find and cost less than for the 413

Here is some interesting info on the dodge RV lines:

Dodge

Could have a 318, a 360, a 400, or a 440. Probably an M-300 chassis.

Check tire dates and anything rubber. Replace if any question at all. Repair one thing at a time until all vital items are confirmed good. Check around as there are forums dedicated to the older Dodge chassis units. They were a lot simpler back then so with or without a manual you should be able to figure things out.

Then they can have fun! Will be heading out on a 7,500 mile trip with my unit in a few weeks.