While making a test a flight i noticed that after taking off and turning on the ap with vertical speed the V/S do not work correctly to make it work correctly i have to engage the altitude hold button and the click again in the V/S button.

When you engage the autopilot after takeoff, it will engage in Level Change and Heading Select if no other modes were engaged first.The plane will climb to the altitude set in the MCP and level off at that altitude.You could select VS while climbing to increas/decrease the climb rate.

thanks for the help mate