When I turn off the engine I'm hearing a hissing, air leak, sound coming from the A/C panel on the dash. I could have sworn I read something about this before but I can't seem to locate the post.

 

The vent doors are activated by vacuum pressure. If you are hearing a hissing sound you have a vacuum leak in one of the lines or the selector. Pull the A/C Heat panel and you will see the lines plugged into the selector.

 

Ok, thanks. I must have knocked something out when I replaced my PSOM. I thought it may have something to do with the EBPV but didn't find anything in the searches.