All of my heat and air conditioning come thru the defroster vents only. What needs replaced?

Asked by Jun 22, 2015 at 10:54 AM about the 2004 Mercury Grand Marquis

Question type: Maintenance & Repair

1 Answer

59,305

Look for a disconnected vacuum line coming from the engine that goes through the firewall. When the system loses vacuum it defaults to defrost for safety reasons. HTH. -Jim

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