I’ve got a Winnebago Rialta Camper on a Eurovan chassis. We did a trip to the Grand Canyon Christmas a year ago and it took 3 hours of idling until we were able to move the shifter in 8 F cold.
Now I’m in Massachusetts with temps merely around freezing: same problem.
Why would the shifter be locked in cold weather? What’s going on here, and is there a permanent fix?
This has an automatic, right? Which engine? When’s the last time the fluid was changed? It might be a balky shift linkage that needs adjustment, cleaning, and lubrication.
from other reading: such problems are either frozen water between parts which ought to move or a problem with the shift-interlock system.
Also: possibly replace brake safety switch and check the gear indicator. the brake switch activates when the brake is pressed that allows you to move the gear selector.
Or: A fuse issue.
It’s an automatic. Last fluid chance probably just before the drive to Massachusetts from Colorado this past July. Hasn’t been on the road much at at since then, was about to get it to a service station for an oil change.
When it wont shift are the brake lights working?
On most cars the shift lock solenoid & brake lights are wired to the brake light switch.
Yes, the brake lights are working (finally a use for my video camera 
I checked the fuses, and the engine has now been idling for an hour, outside temps are above freezing (34F).
I’m now able to move the shifter half way from Park to Reverse.
Does that mean a frozen part is to blame?
‘Frozen’, not by water, but maybe by corrosion or misadjustment. Any way to have a shop look at it?
I’m definitively getting it to a shop - once it’s operable again. Calling for an appointment now. I’lll keep y’all posted.
First check you shift interlock mechanism (noted above). This is a device that prevents you from shifting out of park without the brake depressed. I’m not familiar with this vehicle, but if it is a typical set up then since your brake lights are working the problem either lies in the wiring that goes to the shift interlock or in the interlock solenoid. Given the association with cold I’m guessing that the solenoid/mechanism itself is sticking. Finding it and giving it a good cleaning will likely send you on your way.
My two recommended shops both closed early for Friday, I’ll try again Monday.