The consumer FAQ seems to indicate that it should produce a range of temperatures (see point 3). Update: a note from Delta on this page indicates that it is the temperature that should vary, not the pressure ("handle controls the temperature only, not the volume").
An odd thing about my shower is that when you turn the handle, the pressure changes, but the temperature remains the same. Which means: you can't get a cold shower from it!
My question to you: Is this how it's supposed to work?
Background: I dis-assembled it to stop (unsuccessfully) a leak (the shower-head drips when the valve is off) before using it the first time (I bought the house "used"). And I have since also fiddled with the temperature control gear ("adjustable rotational limit") inside it. So I'm not sure if this behavior is by design, or if it's something I did to it.
Turns out I had put it in with the wrong side on the left/right. When I reversed the valve, the handle started working. It still continued to drip (as it did when I bought the house), and so I replaced the valve with a new one, and it seems to have stopped dripping.