Question: 1986 Water/Heater Control Valve Question

[chris123]

At what position on the HVAC control panel should vacuum be applied to the water shut-off valve? I sprayed it with WD-40, and slightly loosened the 1/4" bolt where the linkage pivots, and tested it with my vacuum pump, and it moves very freely, although no matter what position the slide lever is in (Max, Vent, Heat, etc.), there is no vacuum being applied to the black plastic vacuum line connected to it.........
Regards, Chris

 

[vigman]

Manual or Auto AC

??

 

[chris123]

??

Manual 4+3 transmission.........

 

[vetteoz]

??

The vac operated valve on early cars that isolates the heater core from hot coolant when the A/c is engaged

 

[vetteoz]

At what position on the HVAC control panel should vacuum be applied to the water shut-off valve?

"The temp control slider not only moves a manual cable that controls the temp mixing door, it also makes a vacuum switch (when all the way to Cold)
that "sends" vacuum to the shutoff valve causing that valve to close and not allow coolant to pass through the heater core.

Assuming you have vacuum at the dash control unit (if all of the function doors work - vent, A/C, heat etc.) then check the vacuum line at the control valve -
There should be vacuum out of the control valve with the temp control slider moved all the way to Cold..."