# Switch from vent to defrost?

**URL:** <https://community.cartalk.com/t/switch-from-vent-to-defrost/43408>\
**Category:** Maintenance/Repairs\
**Tags:** cherokee, jeep\
**Created:** [January 29, 2010, 2:51pm UTC](https://community.cartalk.com/t/switch-from-vent-to-defrost/43408 "2010-01-29T14:51:17Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![jeep98](https://avatars.discourse-cdn.com/v4/letter/j/8edcca/32.png) [@jeep98](https://community.cartalk.com/u/jeep98)\
**Post date:** [January 29, 2010, 2:51pm UTC](https://community.cartalk.com/t/switch-from-vent-to-defrost/43408/1 "2010-01-29T14:51:17Z")

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1995 zj jeep grand cherokee 4.0l  
  
 Does any one have an idea as to why ? when I the heats on vent during acceleration it switches to defrost and blows air until to smooth out the acceleration…?  
  
  
  
 Is it a vacuum line some where ?

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**Author:** ![tardis](https://avatars.discourse-cdn.com/v4/letter/t/f0a364/32.png) [@tardis](https://community.cartalk.com/u/tardis)\
**Post date:** [January 29, 2010, 2:52pm UTC](https://community.cartalk.com/t/switch-from-vent-to-defrost/43408/2 "2010-01-29T14:52:58Z")

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It’s probably the one way check valve in the vacuum line between the engine and the AC controls.

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**Author:** ![EllyEllis](https://avatars.discourse-cdn.com/v4/letter/e/f14d63/32.png) [@EllyEllis](https://community.cartalk.com/u/EllyEllis)\
**Post date:** [January 29, 2010, 6:29pm UTC](https://community.cartalk.com/t/switch-from-vent-to-defrost/43408/3 "2010-01-29T18:29:03Z")

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Yeah, it’s probably a vacuum problem