The A/C actually works quite well for its age. It’s just that after a certain temperature it can’t keep up and I’m heavily inclined to believe it’s due to insulation.
The way I can tell is that as the temperature keeps rising outdoors the unit never seems to shut off. I can see on my temperature sensors (smart home life) that the indoor temperature keeps rising despite the A/C cranking away.
Not that it feels hot inside, it’s still around 10°F cooler. It’s just that the minute you turn it off the temperature climbs to the outdoor temperature in just a few minutes.