Stuck brakes

have a 1994 pontiac grand am. disc brake problem- rear left became tight after a short drive, i replaced the caliper and the problem returned. cracked the line loose- fluid was not under pressure. drove the car again, then the right rear brake tightened up (left was ok). disconnected park brake, no change. brakes release after 30 min rest. what is causing this???

Does the vehicle have ABS?