a/c not blowing out the main vent

Asked by Jun 21, 2013 at 03:09 PM about the 2000 Mercury Grand Marquis LS

Question type: Maintenance & Repair

a/c works great, just not blowing out of main vent. defrost and floor work fine

5 Answers


Your heater/ac register controls are vacuum actuated. I would start under the hood and locate the vacuum supply coming from the firewall (right side above or near the black plastic heater case) and trace it to a "T". There will be a vacuum line to the intake manifold (supply), and a vacuum line to a vacuum canister or reservoir. There is also a check valve that allows the reservoir to take over in case of a low vacuum signal (like passing or pulling a hill). I work on Crown Victoria Police Interceptors (same car, different badge, more fun). Usually it's a vacuum supply concern - a broken line.

16 of 16 people found this helpful.

Ac not coming from ac vents

17 of 17 people found this helpful.

Don't know


You could try to see if the solenoids are actuating the control the flappers that change the direction of air flow there's a couple of them. They work off of the vacume system.

1 of 1 people found this helpful.

Most common cause is a vacuum check valve gone bad --located under the hood passenger side this is a unit about $70.00 can be easily changed with just nut drivers. (this is on a 2003 Mer. Grand Marquis.

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