Without knowing which PID you have my best guess is you didn't wait long enough for it to get trained. Think they have to go through the over/under cycle at least 3 times before the unit sets the PID values. At a guess I'd say that'll take at least on the order of 15-20 minutes to accomplish. Once you set AT let the thing kick itself out of AT. At least that's the way my SYL-2352 and Rex C-100 operate. They over/under shoot by quite a bit till they're trained.