My heater valve is not getting vacuum through the black hose with white strip (b/w) in order to open that valve (lever up). After looking through the archives someone mentioned capping off that b/w hose and run a new hose with from the heater valve to the dial controller “out source” in the cabin. He goes on to mention this would disable the auto mode & just work in the “manual” mode. Realizing this isn’t fixing things correctly, Will this give me controllable heat & has anyone ever tried this? I never use the climate control auto mode anyway & don’t want to start ripping into the other components of this complex system.
Larry,
What is the year and what engine do you have in your XJ-S? Jaguar prodused the XJ-S/XJS from 1975 to 1996 and the climate control system design changed over time. Knowing what climate control system is in your car will help others provide suggestions.
Paul
We need to confirm you’re really not getting vacuum. Vacuum to the heater valve is a fairly rare occurrence when things are operating properly. Basically, the system has to be calling for full cold, which is not common.
Paul, it’s a 1991, 5.3, 12 cyl
Vacuum closes the valve. Should only be there when left knob pulled out (manual), and set to minimum temp and system calling for cabin cooling. Valve is probably seized.
Larry …
Quite simply put a vacuum gauge (one of those inexpensive plastic hand pump jobs) on the vacuum line going to your heater water valve. Now go to full cold on your climber control panel. you should see full vacuum, in other words whatever vacuum your engine is capable of producing. That means the valve is being held closed, the default position.
Now select heat on the climate control and the vacuum should decrease or actually go to zero. This allows the heater water valve to open and allow hot engine water to run through the heater core.
If this isn’t happening then your problem is in the vacuum system; the vacuum reservoir or the vacuum solenoids,
Larry,
If I understand you problem correctly it sounds like your heater valve lever is down (valve is open) but you do not have any heat. Is that correct?
As already mentioned vacuum is used to close the valve and not open it. At least that is the way that your car left the factory and assumes that you have an original or similar aftermarket design heater valve.
If your heater valve lever is stuck in the down position you should have full heat all the time. So if this is true, and your engine runs at normal temperature then your heater core is probably clogged up.
To test your heater valve to see if it is working properly you can turn your climate control system on when the engine is warmed up, pull out the left knob to select manual control, and then turn the left (temperature) knob to full heat. The heater valve lever should be down and heat should be coming through the floor vents. Then rotate the temperature to full cooling. The heater valve lever should go up, the heater valve is closed, and you should feel cooler air coming through the floor vents. If the valve lever does not move up and down with the changes to the temperature knob then you either have a failed heater valve (a common occurrence) or possibly a detached or torn vacuum hose.
To test just the heater valve independently you can use a Mityvac or similar vacuum tester (available at any auto parts store), hook it up to your heater valve with a foot or so of small vacuum hose, and pump the Mityvac to apply and release vacuum to the heater valve. With no vacuum the heater valve lever should be down (open and heat position) and with vacuum applied the heater valve lever should be up (closed and cool position).
If your heater valve doesn’t open and close with vacuum then it is rusted and stuck. If the heater valve works properly but you don’t feel hot and cooler air at the floor vents when you rotate the temperature knob then your heater core is clogged.
There was a recent thread about how to unclog a clogged heater cores.
Please write back with more about your symptoms, your results of testing, and whether I understand you situation as being no heat yet the heater valve lever is always in the down (valve open) position.
Paul
Wow, looks like I have some testing to do, at least it’s not a “crawling under the car job” Thanks for all your reply’s. I’ll report my findings .
Larry
Larry,
The first step is to determine whether or not your heater valve opens and closes with vacuum any way you can. If your heater valve doesn’t open and cloae automatically by use of the climate control system then you need to apply vacuum directly to the valve to take the climate control system out of the loop. I have done this myself several times on my Jaguars using my Mityvac hand vacuum pump. If you don’t have access to one or you don’t want to spend money one you could hook up a piece of small vacuum hose to the vacuum nipple at the top of the heater valve, connect it to a engine vacuum line (something like the cruise control), and start up the engine. With no vacuum to the heater valve it should be open and with vacuum applied the heater valve should close. The two attached pictures show the same kind of OEM type heater valve, from my 1984 XJ6 Vanden Plas because I am working on it now, with the heater valve open and closed using my Mityvac. I hope the pictures help.
Paul
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I tested the heater valve by connecting a hose to the manifold port & valve. The lever worked perfect. Actually so does the heater when I followed the instructions you guys sent here, thank you for that. I very seldom (if ever) use the heater here in Florida. I am going to replace that valve with the plastic one Kirby writes about in his Book when I flush the system. My thoughts are valve internal water leaks and effects the AC somewhat.
Larry - - one thing I do – when I remember – is to run the heater on full blast for a couple of minutes about once a month when the car is all warmed up. Try to circulate the coolant and not let it sit stagnate
Good idea, I honesty don’t remember the last time I used the heater in this car. Obviously I forgot how it worked.
The coolant circulates through this heater core virtually all the time, only closed off when the system is calling for max cold.
Thanks Kirby.
I was thinking the heater valve closed off with engine vacuum, unless the climate controls position called for heat.