front drivers side break keeps locking up on 1999 GMC Yukon

my front left (drivers side )brake keeps locking up.i've changed the caliper twice and it hasn't started after i had my main brake line replaced on the front.does anyone have a clue as to what may be causing this.once you bleed the pressure off that one side,you can drive it most of the day without it locking up.the other 3 wheels aren't locking up.thanks

Asked by for the 1999 GMC Yukon
it sounds like you have a collapsed brake hose. replace them both and have the system flushed out.