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Richard, Mercury Technician
Category: Mercury
Satisfied Customers: 15510
Experience:  12 years at a Ford Lincoln/Mercury and Jaguar dealer as a technician and shop foreman.
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Mercury Grand Marquis LS: 05 Grand Marquis AC air coming out

Customer Question

05 Grand Marquis AC air coming out of defrost vent I hear a leak on the passenger side I think
Submitted: 1 year ago.
Category: Mercury
Customer: replied 1 year ago.
(Posted by JustAnswer at customer's request) Hello. I would like to request the following Expert Service(s) from you: Provide Diagrams, Manuals, or Instructions. Let me know if you need more information, or send me the service offer(s) so we can proceed.
Expert:  Richard replied 1 year ago.
Hello and welcome to
The usual cause of this problem is a vacuum leak. When the system loses vacuum it will default to full defrost. The check valve is in the engine compartment. You should first make sure the vacuum hose is still on the vacuum reservoir located under the relay box in the engine compartment. Then you can follow the line as it goes to the back of the engine as the black line sometimes will break near the firewall. If all looks good then go under the passenger side center of the dash and locate the vacuum connector. You should see a white, yellow, blue, red, and black vacuum lines. Disconnect it and start the engine making sure you have vacuum at the black line. If vacuum is present there then we need to check the vacuum at the controller.
Customer: replied 1 year ago.
I checked all that you said there is vacuum at the black line what now I checked check valve two
Expert:  Richard replied 1 year ago.
Yes we need to then go to the vacuum connection under the dash.