Rear Suspension Springs problems of the 2006 GMC Envoy

Rear air shocks that bled down after sitting for extended periods of time. Took to dealer for evaluation and was informed that the air shocks needed replacement. Was also informed that normally the air compressor is replaced also because it is the cause of the leaking. I decided cost was too great so I choose to add springs in place of rear air shocks and was informed that the air compressor would continue to function. Now the air compressor does not work, took back to dealer to find out what the problem is and was informed that once the rear air shocks are removed the air compressor is disabled.