Rick, Welcome! It's great to hear from another Prairie 36 owner!
The boat once had a split system with two compressors and three expansion units that I'm sure worked great, but the guts had been ripped out by a PO, leaving only the registers, thermostats and lots of wire and hose. One expansion unit was over the fridge, and one in each berth.
I ended up going with two 15,000 BTU Dometic systems. One went under the v-berth where one of the old expansion units was, and I used the same intake grill and one 4" duct to a diffuser over the stb side berth. I put a Y on the 6" outlet of the Dometic and ran a new 4" line to a diffuser just to the left of the steering wheel in the saloon. All this was accessible from the stowage area forward of the lower helm station.
The second unit went in the bottom of the stowage area at the bottom of the steps down to the aft cabin. From there it wasn't too hard to run one duct up to the saloon, to the right as you enter the port doorway, and another on the port side of the aft cabin.
None of these are ideal locations, but it's what I could do with what I had. It takes both units to keep the saloon cool on a really hot day, but then the berths get too cool. I hope that getting some shading on the windows and doors helps that in the future. A fan to mix things up helps a lot too.
The two seawater pumps went along the little shelf that the stbd fuel tanks sit on. The breaker panel was already wired for two compressors and I even go to re-use a couple of the wire runs, as well as the two through-hulls for the discharge water. Right now both systems drain to the bilge but I'm working on upgrading to shower sumps for the two showers, so these will eventually go there.
I looked around at other Prairie 36's on the market late last year and early this year. Did you just buy it?