2003 Chevrolet Tracker no 4WD

My 4x4 light comes on but does not engage, there was a clicking sound when locking up front brakes and trying to engage, but now nothing. If the compressor is not functioning will the light still come on. I just had a rear wheel bearing and retainer replaced at a cost of over 400 dollars, I need this vehicle for work, but don't feel that it is worth putting more money into, would like to fix myself