1997 Ford F250 left front brakes locks up

I have a 97 Ford F250 xl, it isnt driven that much but it has at times with my wife and daughter ( hasnt happened to me , yet.) They both say it feels as if the parking brake is on, and pulls to the right but when they check the wheels out, only the left side is hot and smells like burning brakes.Again, this doesnt happen all the time. I will be home soon to look at it, any suggestions? Thanks