I've seen two questions in two days with regard to blowing cold air. One has to do with when the car is at idle, the other has no conditions.
Is it possible to come up with a canonical duplicate for questions like this? It seems reasonable to be able to put together a finite set of conditions and troubleshooting flowchart that incorporates most common causes.
I found one answer that was an exception to the standard set of possible causes in a quick search:
Seems like the "my heater is cold" question comes up often enough -- especially this time of year -- that we could generate something. It might not make sense to mark questions as a dup, but it certainly would be nice to (at the very least) throw a CW link at them in a comment.
I answered a question a while back regarding how the heater core works; it's a subset of the broader question as to why heat might not be present:
Something else to think about with this, isn't this what the site itself is supposed to accomplish? If the answers are out there, we point them to them in the first place and close the new question as a dupe. If tags are done correctly, it's fairly easy to find answers if they are out there.
I think you've effective hit the meat of my question -- do we have an answer enough that has enough solid content that we can build on it? Is the OP okay with converting it into a CW?