Tired - Sorry.
OK: Vacuum pump. You should be able to vacuum out just a manifold gauge set alone without a vehicle to see it pull max vacuum in seconds plus that empties your gauges of air and the hoses.
A compressor is a pump. The #1 reason for a failure to cool is still low refrigerant charge. That in turn if a slow leak will stop flow of oil to compressors. It' s a Domino effect. One even normal paced leak over some arguable amount of time as normal loss of refrigerant once compressor is running dry is already making a mud then can make metallic shards that cannot be flushed out effectively with current condensers the way the flow goes thru them isn't a straight line passage for efficiency works well but intolerant of debris.
A condenser could be made new with a fleck of debris and work just not up to full expected/engineered capacity and go un-noticed indefinitely just written off as a system that isn't as powerful as another - perhaps the whole life of the vehicle?
If you owned a vehicle from new and needed a replacement condenser during your time with it you just might (quite rare) find the repaired system works better than it ever did new and wonder how that could be. It was proven here at this site when a tech here cut open a condenser and found just that on a car owned since new.
Here's a decent YouTube of cutting open an automotive condenser and why they don't flush out or tolerate debris..........
Take this guy with a grain of salt - some would label this guy entertainment up to a total joke but this one I just watched is actually valuable to see what I'm trying to explain, (it's just ~ 4 min.)https://www.youtube.com/watch?v=U0O1mcnwjZs
Problem is stated by this guy too. One problem cause the next such that partial repair is outdated and leads to what I've said you fail again taking out the same new parts trashed again and again.
It's near impossible to really know the exact condition of a condenser of anything like this efficient type. In fact just now searching the web for something even close to what I'm trying to explain just yielded a few demonstrations and explanations that were dead wrong and remain on the web as long as nobody takes them down!
Good grief, you have to know a boatload about HVAC basics to even know what is correct info or not.
I'm trying as best I can. There's just so much to understand it's overwhelming,
(edited later) Just watched that again. It's still good info and video but this genius called the condenser an evaporator in the video! Yikes - can't even get the term of a part correct and it's watched by zillions of people!