Mystery Vacuum Lines
01-06-2022 | 03:07 PM
#2
CF Veteran
Joined: Aug 2020
Posts: 1,798
Likes: 482
From: SoCal
Year: 1988
Model: Cherokee (XJ)
Engine: 4.0L
The black one on the left goes to the vacuum reservoir behind the front bumper (assuming it's there). The vacuum is used to control the vent doors for the HVAC. The one on the right would go to the heater control valve. Since you have no hoses on the core, the heater valve is also gone. The valve bypasses the core when no heat is needed.
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01-06-2022 | 10:22 PM
#3
CF Veteran
Joined: Dec 2017
Posts: 4,074
Likes: 1,128
Year: 1989
Model: Comanche (MJ)
Engine: 4.0
Cap off the one for the heater control valve, and plumb the coolant line directly to the heater. The control valve really isn't needed, failure prone and eliminated in later years.
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