That vent should have a flapper to keep the cold air from pouring into the coach. Not only do they often stick (in either direction), but I found one mfgr. at an RV show that taped them all closed for transport I suspect. The sales guys couldn't figure out why they were so noisy...
I haven't looked for it on ours, but you should be able to get on a ladder and see it from the outside.
Jeff - WA6EQU
'06 Itasca Meridian 34H, CAT C7/350