Central locking and cold weather

The central locking on my 93 Discovery 1 works fine during the summer. However as soon as the weather turns cold the passenger door refuses to lock (until May) It unlocks with no problem but just will not lock itself during the winter months. Ive searched the threads here and cant find one that mentions this problem. Has anyone encountered this or got any ideas please ?

The actuator has a small amount of grease around the small electric motor that may stiffen up with the cold and stop the motor spinning or you may have a iffy connection somewhere due to damp.

Thanks for that adice, i'll have it apart later and take a look.

I had a similar problem, that it sometimes had trouble unlocking in the cold, solved by moving to somewhere warm lol