engine revving up and down when ac is turned on

1999 FORD F-350
183,000 MILES • V10 • 4WD • AUTOMATIC
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CJCOOK21
  • MEMBER
  • 1 POST
the truck idles fine when ac is off but when the ac is turned on the engine revs up and down a few thousand rpms like im revving the engine. Then I turn the ac off and everything goes back to normal. What could the problem be?
Jul 28, 2014 at 10:29 PM
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HMAC300
  • ✓ASE Certified Mechanic
  • 48,601 POSTS
  • ASE Certified Mechanic
check for a vacuum leak like a broken hose etc.
Jul 29, 2014 at 6:44 AM
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