I bought a house a couple years ago but 2 of the bedrooms are always cold. Upon inspecting my ducts for the cold air return, i notice a lot of coated dusts, i am not sure if they are really cold air returns or older heating vents in my house before the system was replaced. Some of them look like they are even blocked off. I don't know if I even have cold air returns.

As for the actual heating vents, I am seeing debris in them, some even looks like dried poop but I can see them well enough to confirm. I need to know what to do next with these problems.