Now temp compressors are the best as they have a habbit of being able to suck down nicely and tend to work at a higher pressur differance.

Second is small power usage is nice, easier on power bill and environment, so I look for mini-deep freeser compressors as usualy they range from 2~4 Amp.

I prefer to have the oil seps there to keep oil from going in or out of the compresser as wzrl said it is not needed despit how irrelivant it was to the design being showen, but for some one making one from scratch, He is indeed correct the intake oil sep is optional if you wont be using it to recycle, IE it will only be a recovery machine with out a large intake oil sep (There is a way around that taking vapour from the first tank holding the old recovered refrigerant and transfering it to a new tank, it achives the same job but you need another whole new tank! the unit I built I just drain the old oil ).

Condencer, any small condencer will do the job, fan of your choice, I pulled a nice litle unit that is forced air off a mide range R-134a fridge (It is going in V2.0 of my recovery unit only I will replace the fan to a 12V type), so keep an eye out for fridges they some times are handly, easpecialy the oil coolers off some of them.

on the discharge side try to keep the tubing as tiny as possibly so it doesn't hold a high volume of refrigerant (I origionaly planned on using all 1/8 for the discharge side, next one it will be this) This should help avoid mixing internaly when you need to recover a dif,, refrigerant.

For your waste oil you can use a ball valve or packless valve, just make sure they can with stand the max expected pressure on the low side, I used schraders on the high side though ball valves would have been much better.

Plumbing: What ever works best yet reduces any stress points and isolates any vibration. The coils you see on my system serve no other purpose other then to reduce vibration from the compressor.

Oil: POE is the best choise for us as it is compatible with all most every refrigerant a SS-Chiller builder/Moder will come accross barring a select fiew, for the ones it is not simply build a second to handle the ones with an oil that will be compatible.

Special Notes:
1- For a unit made to recover small systems an oil cooler isn't required but wont hurt the thing far as long working life is concerned, you just don't want the oil too cool! Passive and small will be more then enough.

2- For systems where it will never draw from a receiver or doesn't need to be a self contained recycling unit as well, an intake oil sep is compleatly optional, If it will be a recycling unit as well you need a tank which can draw liquid & Vapour (& at this point you need a oil cooling method)

3- Lower power is good all round for every thing concerned! A small 2Amp low temp, will do the job, no need to use a 20Hp compressor to recover 12oz of refrigerant!!

(Sod it they don't pay me enough to be perfectly ontime)

4- Pluming the oil drain, Nifty thing called gravity will do the work for you! all ways find the lowest point in the low side to place the drain, and then try and keep a slant going all the way out to the exit point (don't rely souly on the pressure within the system!

5- Over engineering never hurts, they did it with voyager and look how long it lasted, kept transmiting till it got out of range! So go ahead and use oil seps strainers and such, but try to keep it on the low side! We want the high side to have as little volume as we can!

6- Check valves are a nice thing to prevent odd things from happening, if you got one I'd throw it on the oil out line, as last thing we want is to back flush it!

7- Think of it like a SS only open ended, out goes into a tank, in goes through a F/D and to a system, we want it to be low powered as we can reliably get away with. know More about refrigerant recovery system