In my Itasca Horizon all the Dash-AC components you are looking for are up front... above the generator... against the firewall/dash-back-side. There you will also find the amount of 134a (by weight) your coach needs.
The specified amount of 134a includes all the lines and it specified by your chassis builder; however, we always add 10% more than what is called for.
I'm guessing the specified amount will be ~40 oz in total (just a guess) so you would add almost 4-12oz cans of 134a (44 oz). This will not hurt the performance of your AC system and may extend the useful life by 1 or 2 seasons, before you need to add a can. ...But after that you will need to evacuate your system again and start from scratch. The key is to get the right amount of 134a and oil so "entropy" can occur.
* It's very important to get rid of all that old oil too. That is if you want your AC system to work at peak efficiency.
* Good thing you are changing the dryer! You might also want to change your expansion valve too ($25-$40) just because you don't want to open the system up a second time if you find it does not "come to life" after you replace the dryer.
134a TYPE: Just use the cheapest stuff you can find without any additives. Don't buy the synthetic type. That's marketing hype and some use additives of unknown types designed to reinvigorate an old system. But you can do that by changing the PAG oil.
OIL TYPE: There are 3 different PAG oil types. However, everyone typically uses PAG100, because it mixes well with the other two types (46 & 150). However, if you know the oil type that came with your compressor you can use that too. Also we like the PAG100 with "ICE" additive!!!
Note: You will not find the quantity of oil specified anywhere. In all, you probably have 12oz of oil in the system, but that’s just a guess.
Most compressors probably take 6oz. of oil, and then you add 2 oz of more oil per other major component. However, most conventions are based on cars/trucks... so I think you need to add 4oz more for those very long AC lines. (Just a guess.)
Also, most compressors come pre-charged with oil. So what to do about oil? ...Too much oil and your compressor will make noise... too little oil and your compressor will fail prematurely. So use your own judgement, but know it's easier to add oil to your AC system than it is to remove oil.
The process is not hard to bring your AC back to life if you have an evacuation pump and gauges: (Be sure you have the right 134a adapter to connect to your gauge set.)
... and it's anyone's guess on how efficient your AC will work if condenser is not clean.
... last but not least. If your outside air temp is not above 75F it makes is harder for your compressor to turn on.
... The best efficiency I got was a -45F difference between the outside air temp and my dash temp.