The blood pump does not open when the load/unload buttom is push during prime.what could be the causes of this problem

Is the driver motor running? Check long driver screw (sometimes it will losen- actual come off door/arm).

Also, If this C-3 is a re-pack (2nd generation), check the 501 (or 301) fuse. I haven't worked on a C-3 for a couple of years, and no manual available; I may be incorrect in the numbering. However, Its the fuse on the inner wall (behind the power distribution board), and just above the power supply. One more thing, I have a friend that has a boatload of new spare parts for these machines (i.e., pumps GP-1,2&3, etc.) ask your medical director if he/she is interested in them. I'll check back in a week or two for a response.
Goodluck with all your endeavors,

Or.... check the stopcock on the vacuum line. Sometimes... they get in the wrong position. If not, refer to the other solutions, they are right on baby.

The load/unload feature is available only during Autotest,Setup,and Rinseback modes only