1997 Ford Mondeo central locking

Noticed locks would all close when fob activated but immediately opened again. Only when the air temp. is low. Have to lock doors individually. When normal air temp. locks seem ok but one door refuses to unlock / lock. When it was very hot last weekend all doors worked until next morning when the one door (offside rear) failed to lock / unlock again. Often doors would unlock themselves at any time or place which results in the alarm sounding if a door is opened. When manually locking the car if the key is turned accidentally the wrong way all doors (with the one exception) open again.