You will have to check your manual to be sure. I am not sure about your 385HV but on my 383, which I believe is similar, I have to be in Manual flash mode and adjust my flash via the power settings. Under most circumstances I use 1/4 or 1/8 depending on the situation.

This may or may not help. I love my old 283 and my 285, but I do know that the 383 works differently then either of those flash units. They were much more autonomous and worked off the feedback from their own thyristor. The 385 was really designed more for the modern camera systems. Your own camera may be the problem if it is not set for using flash all the time. It may not even be sending a signal to your flash to fire at all. You may have to go into the flash settings on your camera and set it so the flash always fires. It is not quite as convenient but it still works quite well. If your camera allows flash compensation, which would work well for daylight fill, then the 385 may be expecting that signal from the camera itself.

I don't know if this makes any sense, and you probably know all this, but these are the things I would try first.