doug has it right. the pic you posted shows a hwh hydraulic pump and tank.
it is not even remotely related to a chassis a/s system.
you are about to cause yourself a very expensive problem.
if you dont know this, you should consult someone who does.
information is free, all you have to do is ask.
download a service manual for your chassis a/c system. its available on the internet. sometimes totally free.
chassis air is notorious for not cooling enough. have the pressure checked by a local shop. ask if they are equipped to do the job of repairing the a/c system. truck shops are a good place to call. if they work on rv;'s.
dont proceed if you dont have good information. its very expensive to just throw parts at it.
i dont mean to be preachy, but this could get very pricy.