A/C Blows thru windshield

[Chuck C.]

My 97 Sig a/c blows thru the defroster vent against the windshield. I went under the hood & found an unattached vacuum line wrapped around the master cylinder. When I put my finger blocking the hose, the a/c vents blew cold air normally. A few seconds later, the cold air blew from the windshield registers again. My mechanic re-attached the line to the bottom of the electrical relay box next to the brake fluid reservoir. The a/c blew correctly for a few seconds then went back to the windshield again. What's wrong?

Chuck

[Jet Set Limo]

Quite possibly, it's the check valve located on the right (passenger) side on the firewall that needs to be replaced or a vacuum leak elsewhere.

[Tman70]

That 'relay' box has the vacuum reserve tank built into it. Use a vacuum pump and test it to see if it is leaking.
Also look here...
http://www.lincolnsonline.com/tech/00130.html