I'm trying to create a moving platform for a simple platforming game in AS3. The platform starts moving when you activate a switch. The problem is I can't set the boundaries for the platform correctly. It should bounce between 60 and 436 on the X-axis. I'm not sure what I'm doing wrong. When it gets to the left boundary it just stops. Here's the code.

if (greenSwitch == true)
{
lift.vx = -5;
lift.x += lift.vx;

if (lift.x < 60)
{
lift.vx *= -1;
}
if (lift.x > 436)
{
lift.vx *= -1;
}
}