Re the heater water valve on the XJS firewall center: At full cool, vacuum is applied, which moves the lever on the vacuum servo UP, cutting off water flow.

At full heat, (no vacuum) the lever is meant to go DOWN.

My question is: By what means does the lever move DOWN again in the absence of vacuum? Is it by coolant flow action, or is it spring-loaded, or how?

Because mine does NOT return to the DOWN position in the absence of vacuum, as it should.

If you move it down manually with a screw driver (it moves very easily) then you get coolant flow, and heat again.

In the morning, when I first fire up the car, you can hear lots of gurgling under the dash, like the coolant is flowing but maybe with some air in it. ? Coincidentally, in the morning is the only time I can get any heat to come through the system. Once the selector is turned for any A/C, it is not possible to return to heat mode, and I think this valve is the culprit. But I need to know how it works, as above. Thanks!

 

1st time jaguar owner here. I have a 1984 xjs h.e. that I just bought on Friday with the same issue. I don't have a clue what I'm doing, so I just want to say thanks for asking the question and for doing the research. I'm going out now to start the car and see if any of the things you mentioned work on my car. Heck, if I have to I'll tape that valve down just to get some warm air. Blower works great!

 

Okay,
The rudder, flaps, and heat are working again...but just like kirby's book points out...the heat went away in about 10 minutes. I'm looking under the dash for the in-car air temperature sensor. I'll let you know what I find out.
rookie

 

Well that was kind of silly, i went in from the left side of climate control panel only to see a bunch of wires and not really know what I'm looking for. I'm going to post a new thread and see if anyone knows exactly where this "in-car air temperature sensor" is.

 

I got my heater valve "un-stuck" with Tri-Flow aerosol lubricant, so now I get heat in the car...although it's a "weak" heat, it at least keeps us from freezing to death.

And, the climate control in its wisdom, even at full heat, blows 70-degree air at your legs (cooler air than is coming out the defrost and facia vents). I guess it figures your legs need to be cooled for the next time you break down and have to start walking.

Appreciate the posts...Let us know how your Einstein-meets-Rube-Goldberg system turns out, and I'll do the same....