OK, I'll give it a shot.

Compressor looks good to me. If it's quiet and capable of generating 275 on the high side, it's definately doing some compressing. No problems there.

I can think of three possible problems.

Is the high side restricted, limiting the flow of refrigerant to the evaporator. Feel the high side line - it should be hot all the way to the expansion valve. If it turns cold at a point before the expansion valve, you've found the problem.

Could be a bad expansion valve. I usually replaced these on spec when the system is apart, they're only 25 bucks or so.

Any possibility the evaporator is restricted by leaves or dirt in the air path? If part of the evaporator is blocked it just can't extract the required number of BTUs from the air flowing over it. Result - slightly cool, muggy air.

That's all that comes to mind. The high side pressures look good, the low side look OK at idle, but is higher than I like to see at 1500 RPM.

- JimY