Make sure your tuner is set to "automatic" mode. That could be your problem. And.. I use AM mode for tuning.
You may need to use more power for tune up. You said "I read the manual". Which one--txcvr or tuner? Check BOTH carefully for operating guidelines
I have an MFJ-901B (non-automatic) tuner. For my Icom IC-718, as per the Icom user manual, I must use RTTY (or CW) and a minimum of 30 watts
for manual tuneup using the radio's SWR meter.