If I'm not mistaken it only acts at higher flaps settings. To my untrained eye it seems they never got this far.
The Boeing 737 Technical Site
A flap load limiter (-3/4/500) / flaps/slats electronics unit (-NG) will automatically retract the flaps from 40 to 30 (-3/4/500) / also 30 to 25 (-NG) if the limit speed is exceeded. The flaps will extend again when speed is reduced. This feature is on all aircraft even though the FLAP LOAD RELIEF light is only fitted to a few.