# Vacuume wipers and ac vents **URL:** \ **Category:** Maintenance/Repairs\ **Tags:** b3000, mazda\ **Created:** [July 19, 2010, 12:53am UTC](https://community.cartalk.com/t/vacuume-wipers-and-ac-vents/52089 "2010-07-19T00:53:43Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![jeffjb](https://avatars.discourse-cdn.com/v4/letter/j/b9bd4f/32.png) [@jeffjb](https://community.cartalk.com/u/jeffjb)\ **Post date:** [July 19, 2010, 12:53am UTC](https://community.cartalk.com/t/vacuume-wipers-and-ac-vents/52089/1 "2010-07-19T00:53:43Z")
My ac vents close when I go up a hill and open when I go down the hill and decelerate the vents open allowing cool air into the cab. It reminds me of my old Jeeps with vacuum wipers. When you go up a hill they slow down to almost a stop but when you decelerate the go like a bat out of hell. ---
**Author:** ![PvtPublic](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/pvtpublic/32/13089_2.png) [@PvtPublic](https://community.cartalk.com/u/PvtPublic)\ **Post date:** [July 19, 2010, 1:18am UTC](https://community.cartalk.com/t/vacuume-wipers-and-ac-vents/52089/2 "2010-07-19T01:18:58Z")
You have a vacuum leak in the ventilation control system. Most likely the the blend door actuator or line to it. ---
**Author:** ![kizwiki](https://avatars.discourse-cdn.com/v4/letter/k/7cd45c/32.png) [@kizwiki](https://community.cartalk.com/u/kizwiki)\ **Post date:** [July 19, 2010, 1:27am UTC](https://community.cartalk.com/t/vacuume-wipers-and-ac-vents/52089/3 "2010-07-19T01:27:59Z")
Your a/c is a closed and independent hydraulic system when it is working right. But your cabin vents are likely controlled by vacuum. I can only guess that you have a slight vacuum leak that might get worse as you ascend a grade and improve as you descend. Moisture in the system might be the cause. Your cabin’s vents might be opening and closing according to altitude or just pitch. I think this is likely. I can’t recommend a solution, however.