AC problem

Most of it stays in the compressor. Whole system only needs about 4oz

 

Something's screwy. The low side will drop and high side will build when the clutch engages.

 

3.5 lbs added? Per ID info tag on Truck? Sometimes it’s possible to be a bit low and fan reduces pressure before pressure switch has a chance to kick it off. 3.5 sounds a bit low. Freightliner is 3lb 7oz. Paccar usually higher. No idea about International. 3.5 lbs. = 3lb. 8oz.

 

250 at 85f seems good to me for the high side, but the low side should not hit 250 ever. It should be 45 to 55ish. Static, after the truck sits a few hours, the pressures should equalize somewhere near 70ish.
Definitely wait for the expansion valve. You must've used a R&R machine to push the refrigerant in?

 

High pressure switch should disengage clutch. Regardless of what’s causing the high pressure.

 

Charge should be 3.75lbs. Even with a slightly low charge, it should still cycle. Does the compressor disengage if you simply turn the ac off? To allow the compressor to be powered, the high pressure cut off switch must not trip, low pressure switch not trip and the freeze probe must not trip. These need to be checked. The next question is if this truck as an AC APADS module or not because the wiring and switches are different.

 

I slept on this. By chance were you measuring pressure with a manifold gauge set and if so did you have both high and low valves on the gauge set open? If you did you basically tied the high and low sides together and that could explain why both high and low pressures were equal when running the A/C.