Hello, I have an old single knob shower faucet that needs to be adjusted. It operates by simple rotation. It does not have separate movement angles for pressure and temperature. You must rotate the knob until the pressure is high enough to take a shower. However, by that time, after 10 or 20 degrees of rotation, the water temperature is already too hot. The only way to get cold water is to turn it to a very small trinkle. From what I have read, it should not be hot until at least 90 degrees or so. I need to get close to full cold water pressure before blending in the hot water. I tried adjusting both of the large phillips head screws, both tightening and loosening. It does not seem to affect the ratio. I have no idea what the little plastic unit with the hex screws is. I did not have the proper screwdriver to adjust them. Here is a picture. Uploaded with ImageShack.us Any advice?