Clutch slips after engine warms up

[tbirdtbird]

The low side gauge indicates to me at least that you are somewhat low on refrigerant.

While you are at it measure the clutch gap, it s/b no more than .020

[JohnHere]

The vacuum oil was not replaced but was clean in the sight lense. I have only used this vacuum pump one other time, a few years ago.

The oil might look clean in the sight glass, but it could still have moisture in it, picked up over time, reducing the efficiency of the vacuum pump.

Or even better than a Manifold Gauge Set (MGS), use a micron gauge and ensure that it reads +/- 500 microns when you're done evacuating the system, again depending on your elevation.

Yeah and one of those fancy shop style AC tools with all the push button features built in!

FYI, you can buy a new digital micron gauge, a well-known brand that some pros use, for less than $200.

As for the oil, should I redrain everything and refill exactly? What about the oil in the dryer and other nooks and crannies? Where is the best place to add it? What about adding to an already charged system? Sone youtuber said you had to add half the amount to the compressor and have to the evaporator to keep the compressor from sucking a large amount of oil at once. He never elaborated how he added half to the evaporator, its not like you can just pour it in there without it going all over the place.

It's called "oil balancing," and the subject has been extensively discussed on this Forum in the past. Too much to re-create here.

Learning about AC system work seems to be particularly annoying because the sheer amount of click-bait and wannabe youtube know-it-alls seems to add an extra layer of cloudiness to getting to the real knowledge.

MVAC is not as simple as some on the Internet would have you believe. Posting your questions on this Forum is best, IMHO, because you'll find on here a number of certified professionals who have been in the business for many years, as well as other well-informed people, who know the subject inside and out. You can always trust that they'll give you their best advice.