When weather is cold cruise control doesn't engage..

[Az4x4]

During warm weather the cruise control on my '03 Ram 2500 4x4 5.9 works as it's designed to. But once we get down to freezing and below the cruise control indicator light comes on but it won't engage and maintain speed. Any ideas where I should start looking for a solution? What components might be affected by cold to the point they quit working? Thanks for looking. If you've experienced this problem and found a solution I'd appreciate hearing from you..

 

[Ozymandias]

Does the Electric vacuum pump work as desired? That would be my point to start from as the On-Light indicates working. So the electric side isn't my first way to check.

 

[Prairie Dog]

Vac pump would be my first guess too but have to ask Auto or manual trans?
If manual, no vacuum pump.

 

[Az4x4]

Yea, it's an auto. Soon as I have a chance, this afternoon if the rain and snow holds off, I'll check out the vacuum pump. That cruise control doesn't engage in cold weather but will engage when the weather is warm is more a nuisance than a problem. Still, I want to get it figured out and fixed, so thanks for the suggestions so far..