'99 OBS Suburban with rear A/C, R134A capacity?

[me88]

So reducing the charge to 3 LBS 8 OZ makes the system barely cool at all anymore. So it is currently filled at 4 LBS and cools okay-ish, guess it's better than nothing

Still makes me wonder why the slow-leaking OE compressor worked so much better than the new one, my guess is that the system is overfilled with oil since they didn't mention doing anything with the oil volume. I was told "we always just put them in the way they come", but the box had instructions for oil balancing which they ignored. My research tells me that excess oil is impossible to get out unless you replace all AC components since it sticks to the walls of all the components.

This reminds me why I always hate going to workshops, they almost never ever do the work right.
Should have gotten an AC certificate and do it mightself in hindsight

 

[OR VietVet]

So, no flush, bad decision. The 3.5 pounds sticker does not take in to consideration that has rear a/c. The a/c part you install does not know that. Excess oil can get out with a flush.

 

[me88]

They told me when they took the lines off the old compressor that they were clean (no grey goop) so the system was not contaminated. I'm sure they did not do a flush then, the bill only said evac & charge.

Googling tells me that there are two different kinds of AC flush techniques available:
- Fill and evacuate with liquid R134A a couple of times (works with commonly used AC machines)
- Evacuate the system, then use a flushing liquid together with compressed air, then dry the system with nitrogen (needs special hardware)

3.5 LBS was the original sticker on the vehicle, the picture I took of it says:
Use only R134A or equiv
Suburban 3 lbs 8 oz (1.588 kg)
Yukon/Tahoe 2 lbs 12 oz (1.247 kg)
and Synthetic Oil #12345923 ...

 

[OR VietVet]

The second one is how I used to do it.