I having do different problems with the a/c. First being if I dont use it for a few days then go to turn it on it causes the engine to go to 500 rpms then jump up the 900 until the compressor goes off.
That could also be caused by a bad IAC. I had the same issue. As long as the compressor was running, it would be fine. As soon as the compressor would kick off, most of the times, RPMs would drop to 500 and the engine would stumble. I also noticed that as long as I was on fan speed 2 or higher, I didn't have those issues. If it was on fan speed 1 (the lowest setting), it would exhibit this problem 95% of the time (At idle and in gear (At a stop light), in park and just idling, etc). I have no idea about the noise you are hearing.
The throttle position sensor is responsible for telling the PCM that you are at WOT. It may not be showing the proper voltage and thatís why your ac compressor isnít turning off. Sorry I can't be more help with that, maybe Bob, rwenzing, knows more details.
I know that on some Rangers, even with the pedal all the way to the floor, the butterfly valve isn't open all the way. There is a "mod" to fix that by taking some of the slack off the throttle cable by tying it with a zip tie (Search the forums, Iím sure you will find a lot of information on that). There is an easy check for this. Have someone depress the gas pedal, with the engine off, all the way to the floor while you have the intake off and look at the butterfly valve.
You have a 2004, isn't it under warranty? If it is, take it to the dealer and have them fix it. All of what you are describing should be covered under the 3 year, 36,000 mile warranty.
You shouldn't have to be adding freon and lube to a 2004 AC system. If it's a bad bearing, oil wonít help, only a new compressor will.