The compressor clutch won't pick up if there are 4 conditions, dual pressure switch and rotor lock detection being two things that will prevent the clutch to engage. I would avoid using cans and use a guage manifold set. Pressures should be 40 psi on low and 140-150 on high i believe. Open the glove box and take it out. Try the control functions to see if the noise is related to one of the three servo motor systems. They are plastic, need greased maybe and are common to be noisy when they fail.