2019 389 Pete HVAC issues.

Hey y'all, I would appreciate any insight you could share about the air conditioning troubles I'm having with this truck. It's a 2019 Peterbilt 389, Cummins X15 Efficiency Series, Fuller Advantage automated transmission, 280k miles, 10,600 engine hours.

1. The A/C blows 50° at 800 RPM when idling or running the PTO, but when cruising down the highway at about 1350 RPM the compressor clutch unlocks after about 15-20 minutes and does not re-engage unless you stop the engine and restart it, or idle / run the PTO. I have tried shutting the cab and sleeper A/Cs off for 15 minutes and then turning them back on but that doesn't do anything. All fuses test good.

2. If I run the cab blower on its highest speed it will shut off after a few minutes. It will restart if I move the switch to a lower speed setting. Also, I can run it on the second highest speed with no problem. This happens regardless of whether I'm using the A/C or the heater, and regardless of where the air is being directed to.

FWIW, I always have it in recirculate mode unless I'm running the defroster, and I normally have it blowing air only out of the panel vents.

Any idea what could be causing either of these issues? Thanks in advance.

Edit: this truck is not equipped with an APU, bunk heater, or anything like that.