Goldenrivett
In FLCH, AT it is programmed to give either Climb or Idle and it does not expect to change until approaching the level set.
Actually FLCH is more clever than that. It utilises a time target of 120 secs to achieve required level change and adjust thrust to so do. i.e. increases/reduces sufficient thrust as required-just as a pilot would. If it cannot achieve that then it sets CLB or IDLE as required. This is particularly evident when being stepped down 500 ft or so by ATC during intermediate approach. Of course you simply manually override if its not doing it quickly enough.
Mind you this was a 100 or so years ago (80s-90s) and reading the various comments above, its just possible that's changed but I think unlikely.