I am talking about the hot water valve right dead-center on the firewall, the one prone to failure. Is this supposed to have vacuum being applied all the time? Id vacuum applied mean water off? Where does this vacuum originate? Is the hose end located under the intake manifold? I plan to replace the valve with a plastic substitute that I have heard works very well. I've got heat on ALL the time. When I ask about vacuum all the time, that is with the temp set to 85 inside the car. My AC is working based upon condensate dripping, but I've yet figured out how to get the center vent to open. I'm hoping that researching some of these vacuum connections will help with this too.
Thanks Much.
PS, I've included a link to pics of the car. It's only marginally for sale. I usually have all of my cars up. Right price anything can go :-)

Submitted by r.magowan@cox.net on Fri, 07/22/2005 - 06:56

Actually there's no noise whatsoever when moving the temp control knob. It does go into defrost mode though. The last time I was testing it I let the engine warm up a bit and I do get the blower fans to turn on at the other speed settings as long as the engine temp is up. I'm not sure which fuses to check for the other (servo?) action. I have the side cover off the right side of the footwell and am trying to ID the AMP but not having much luck. I'm a bit reluctant to tear into this area as I've no clue what I'm doing. I will see if I'm getting vacuum at the valve; I have a replacement on order anyway. The climate control servo and the amp need to be examined if I can find them. I will eventually, I just need to go slow. I'll probably have the AC working perfectly by the first snow fall. Thanks for advice folks.

Submitted by dougdwyer@adel… on Thu, 07/21/2005 - 22:58

Vacuum *closes* the valve to give cold air. No vacuum *opens* the valve to give hot air.

The supply hose enters the firewall in an area just below, an inboard of, the battery. It goes to a vacuum switch on the climate control servo.

If you have vacuum to the valve (do you?) it should close (you can watch the lever arm actuate on the heater valve). If it doesn't close it is seized.

If cold air is called for and there is no vacuum to the valve then the hose is leaking/broken/disconnected or there is a fault in the control system which won't allow vacuum to be applied.

When you operate the temperature knob does the system respond with whrring and clicking ?

Doug Dwyer
Longview Washington USA
1987 XJ6 Ser III
1988 XJS V12 Coupe