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I have an 89 s10 4 cyl 5 speed which has a vacuum controlled heater control valve , previous owner had hoses to heater core blocked off due to bad heater core which I replaced. My problem is he also disconnected the vacuum line to control and now I can’t find any place to plug back in to get vacuum. Should it go back through the dash and connect to one of the ports on the back of heat/ air selector?
 

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Back in the day I remember that the control valve was operated by the heater control in the dash. When you select the cold function its supposed to shut off hot coolant flow thru the core to enhance the AC cooling function. See if you have a vacuum port on that control unit in the dash. No guarantee on this info. ;)
 

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Most definitely back to the control.
 
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