The car lock broke down

The driver side door's lock and actuator which comes together was faulty and took the car to the garage to fix it. They have opened the lock and fixed back now it works, but the problem is that they do not know what caused it, as I could not open the lock and when opened from interior I could not lock it anymore. Our suspicion is that the actuator which does not work well on cold winter time has been blocked. I also have read that many Ford Focus face the same problem: actuator and lock faulty, they are no good in winter time. At this moment it, works but not sure for how long...