I just finished a complete repair of that system.

It's quite odd that the defrost is not providing any flow. The reason for this is the fact that the defrost flaps default to the open position. Vacuum is required to close them. On all other vacuum doors, they require vacuum to open.

If there is no defrost air, you need to check to see that the vacuum door is working properly and not stuck in some fashion. You can also test the vacuum pod for the defrost while you are in there.

The procedures that TX sent you should show you the location of the defrost pod. This pod is accessed via glove box removal.

While you are there, you should remove the carpeted liner on the right side of the transmission tunnel and check out each vacuum circuit to be sure that you don't have any other pod issues. There are six circuits that feed six pods. However, some circuits (#3,#5, and #6) feet two pods on the same line.......so, you have to be careful of your results.

In my case, two of the dual pods were NG and I bought OEM replacements for them.