If the refrigerant system is low enough on refrigerant, the ECON light will stay lit, and the compressor will refuse to engage. This is, as stated, a self-preservation control. PLEASE be sure to not only evacuate the system REALLY well, but also inject the proper amount and type of oil into the compressor - IT DOES NOT COME LUBRICATED.
For the record, my best friend just did mine not too long ago, as he's a God of Audiness. I picked up a brand new OEM compressor itself for under $700, shipped to my door, so please don't pay the stealership what they ask. I also got the drier for I think it was $45. Oh, and don't forget to replace the little filter tube, otherwise you're going to have metal shavings in your brand new compressor.
As stated previously, it's a bitch of a job, but if you're *very* comfortable working on your car, you'll get it eventually. For the record, the drive shaft had to be torched off of my compressor. And just as designed, when the compressor failed, the safety input connection snapped. You'll know what I mean when you take apart your old one.