testing air compressor

Was wondering how do disconnect the air compressor to see if it is the cause of compression in coolant system. If I disconnect the coolant to the air compressor I will lose coolant and the compressor will not be cooled...right? if I disconnect air it will still be pumping air into coolant? Confused on how to see if the compressor is bad before I tear into the engine. By the way 2001 w900 caterpillar c15 6nz

 

did some testing today. bubbles with air compressor connected and disconnected. funny thing is the overflow tube can't be more than about a 1/4 inch into the water any further down and it does not blow bubbles? posted a you tube video called "bubbles" link is below. that was with the engine at operating temp and idling. also noticed steam coming out of overflow tube when pulled out of water. Coolant hoses hard? A lot of pressure on radiator cap, blew out a lot of coolant when I loosened cap. also noticed some gurgling bubbling noise coming from back of water pump after truck was shutdown. Would water pump or thermostats cause compression in coolant system they are bad? http://youtu.be/ZZaKPTMPr-A

 

same thing...at 1400 rpm top speed cruise will set. Bubbles only when bottle is turned sideways a little or hose is about 1/4 to 1/2 deep in water never with bottle straight up and down. No sludge/water in/on oil cap or blowby tube from valve cover. One thing I did notice was once I turned cruise off and brought truck back down to idle that is when the coolant comes out of the overflow hose and cap. Put a new cap on also. I am confused. Could a water line being plugged cause this. Really grasping now, do not want to tear into this engine without be absolutely sure.