Start with the simple stuff first. Did you check the fuse in the fuse box?
Some people have installed an inline fuse on the pump to protect their CCU. Perhaps a PO did this to your car. Check the wiring on the pump as far back as you can go.
Also, how do you know it does not get power? I'm not 100% positive when it kicks on but if you turn your CCU to full heat it should be running.
2000 E320 4Matic Wagon
1994 Chevrolet 2500 6.5 Suburban