I recently had some problems with a lens, the autofocus stopped working in cold (but not freezing) conditions. The lens exhibited very similar issues, but on a more permanent basis, when I first got the lens just over a year ago. At that time, I had to send the lens twice for repair before it would start working properly. They replaced an internal part the second time and it seemed to work when I got it back in February 2012. I used the lens happily during the Spring and Summer in warm climates but when it got cold in late Autumn, the AF started acting up again.
After a bit of testing, I was quite certain the problem was with the temperature of the lens and wasn’t due to the camera (tried it on different bodies with the same result). The critical temperature seemed to be around 5 degrees C below which the lens would stop focussing properly. It seemed as if the clutch connecting the focus ring to the lens wasn’t releasing properly preventing the lens from autofocussing. It could have been due to an electronic part or mechanical interference due to differential thermal contraction. In any case, the lens had to be sent back. Of course, the warranty period had just expired so I wasn’t terribly hopeful that I could get the lens fixed for free.
After a few weeks, I got a message saying my lens was being sent back. I was pleasantly surprised that I wasn’t going to be charged for the repair. The box I received looked a bit bigger than the one I sent. Opening it up, I saw that instead of repairing the old lens, they’d sent me a brand new replacement. So I have to give a big thumb’s up to Sony for this customer service interaction. It makes up for the lens faults in the first place.