1988 Mercury Grand Marquis blows hot air when accelerating uphill and downshifting. Does this with or w/o a/c running. What is causing this?

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Asked by Apr 03, 2012 at 01:52 PM about the 1988 Mercury Grand Marquis

Question type: Maintenance & Repair

The a/c will temorarily blow hot while downshifting during acceleration. Also, warm air comes out of vents w/o the a/c or ran running during acceleration and downshift. Vacuum issue? Otherwise, the a/c and compressor work normally and blows cold.

1 Answer

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Very possibly vacuum issue. Hook up a vacuum gauge to manifold vacuum. If you can run gauge inside car while driving and reproduce symptoms and watch gauge you should be able to confirm or eliminate vacuum issues. You should have 17-21 at idle. Look for steady and proper vacuum while driving. No load high vacuum loaded lower vacuum, but steady.

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