In the photo is a vacuum hose. It comes out the space just behind where the windshield washer fluid container would be, and it tees to the full throttle vacuum switch and somewhere else. Is the "somewhere else" the heater control valve?

Thanks!

John
1987 XJ-S V12

 

Yes, I believe that hose goes to the heater control.

 

JCR

There should be TWO vacuum hoses emerging from the panel below the washer fluid reservoir. One, with a non return valve in it (as in your photo) keeps the aircon vac reservoir 'topped down' with vacuum. This hose goes to the A bank manifold and includes a T off to the full throttle switch. So the free hose you show should be connected to the spigot on the manifold end.

There should be a second, slightly smaller diameter, vacuum hose emerging that goes straight to the water valve in the centre top of the bulkhead. This closes off the hot water when full cold is asked for, so the aircon is not fighting heat from the hot water in the unit under the dash. The aircon unit vacuum solenoids activate this tube. It is not connected to anything else under the bonnet except the heater valve. In your photo there seems to be a non-standard-looking item where the heater water valve usually goes, perhaps someone has altered the system? If so, OE heater water valves are still available, or maybe the aftermarket item in the photo has a vac activation to close it like the OE item?.

I think I can see this second tube in your photo, but it appears to be going in a forward and downwards direction, rather than to the water valve. If I am mistaken and this second tube is not visible, then undo the plate and look to see if it is under there somewhere.

Greg

 

Thanks Greg, you were spot-on. You can just see the other hose at the bottom of the picture, looking at it now I'm not sure how I missed it!

I've replaced the original metal heater valve with an after-market plastic unit, which is what you see. I need to get an adapter to step-up the vacuum diameter to fit the new valve now that I know which hose attaches to it.

Thanks again!

John