heater valve

[sandmtnjeep]

I am just trying to understand how the heater valve functions.  I replaced the heater core and am checking out the rest of the system.  I am getting no vacuum at the port on the valve.  What position should the heater controls be in to have vacuum?  Also my temperature gauge reads extremely low is this normal?  Thermostat was replaced as well as the radiator cap.  Thanks for any help.

[DAVE]

I think you will have vacuum there when you turn on the A/C diverting water around heater core instead of thru others will reply if this is wrong also my temperature gauge just gets up to the edge of the green, so very low

[sandmtnjeep]

Thanks, that is where my gauge reads also so no need to change the sending unit.  Where does the vacuum come from to operate the valve?

[amarshall]

Vacuum for the heater valve comes from the HVAC control head.  There should be two lines going through the firewall, one from the vacuum source to the HVAC control unit, and one coming back out to the valve.  There is a switch on top of the control head that should send vacuum to the valve when the temp slider is at the far left (cool setting) OR when the A/C is on.  Apparently these switches frequently crack and create a vacuum leak.

[sandmtnjeep]

Thanks for that good info.  I'll check the lines first then if necessary look at the control head.  Are these available anywhere?

[amarshall]

The control heads would only be from a salvage yard (or kind Samaritan) at this point.  Good news is that the vacuum switch portion is modular, you can take that off the bigger head assembly and replace just that piece.