The front left caliper is locking up on only the left wheel 2003 Honda Accord LX?

My front left caliper keeps locking up on that wheel only. It gets very hot and starts to smell like wires are burning or something and I have actually had smoke coming out once.I have changed the pads on both sides and the rotor on the left side, also have changed the caliper twice thinking it may be faulty and its still happening. This weekend we changed the brake hose on that side and its still locking up. My neighbor mentioned that it may be the proportioning valve or the master cylinder but I'm doubtful on the master cylinder because I still have brakes on the other three tires and I'm not really sure that the proportioning valve would cause a problem on one side only. Please help I'm really not sure what the next step should be. And I haven't driven the car because of this problem in two weeks aside from test drives I've been bumming rides to and from work. Thanks in advance!