I bought a used 2006 Greyhawk GS last May. I used it for a hunting trip fro October. Thru end of Dec. Had problems with getting heat out of the vents. Checked to make sure everything was running properly. While looking at the vents, I noticed there was a layer of something similar to furnace filter fabric installed below the metal vent covers. I removed these and had full flow of heat coming from vents. I am thinking that the gauze type fabric was meant to keep debris from getting into the duct work by dealership. Once removed there was plenty of heat.
Prior to removing the filter type material, I could feel heat trying to come out of vents, but it was very restricted.
Is it essential to have the vents filtered in this manner? I don't know, but I needed the heat as temps were typically at freezing and we'll below.