1992 Mercury Grand Marquis Q&A
1992 Mercury Grand Marquis Question: why does air only exit through the dash vents only.
Your air ducts are not connected. Look under your dash and re connect them. If the connectors or snaps are broken, duct tape the ducts to the vent windows. Good Luck. - timwbenz
I would also check the heater box to see if it is cracked or broken causing blend door not to operate properly - goodguy