Hi I have a 1986 XJS with a Lower Heater Vent that Always Blows Cold.

With the heater on (85deg), regardless of fan speed setting (low/auto/high), the top face vents blow hot air, but the lower vent is directing cold air to the feet.
With the heater in the cold 65deg position it also blows cold air.

I don't think it should do this, atleast not when heater is set on hot position.

Its had a new a/c amplifier and heater core and tap. Cooling system is bled. Engine and Electricals in good health.

Any ideas? Where should I look first?

Thanks

 

I've moved your post from General Tech Help to XJS forum.

Members with the same model as you have are the ones to be able to offer advice on the heater output.

I've left a redirect in General Tech Help so you get two chances!

Graham

 

First a couple of questions.

When you change temp settings do you hear a slight whirring sound from behind the dash? You should.

When you select "85" does almost all of the air flow come thru the footwell vents? It should.

When you select "65" does almost all the air come thru the center dashboard vent? It should.

When you select "85" are you getting zero vacuum at the vacuum hose to the heater valve/tap? You should.

When you select "defrost" do ou get max fan speed and hot air to the windhshield? You should.




Since the amplifier is new I *suspect* the servo is not operating all the internal flaps correctly.

All incoming air is first chilled and then heated as needed. These means air comes thru the evaporator core for chilling/dehumidifying and then thru the heater core for heating, as directed by the internal flaps.



Cheers
DD

 

Since we're here talking about vents...

So Morris likes to throw hot air at me when I don't have the climate controls turned on. The fans are not on, but there is hot air still coming in from the vents. It's a nice "feature" when it's cold outside, but not so nice in the summer. What gives? Are my vents stuck in to let fresh air in? American cars often have a feature to select either new air or recirculated air for the vents. XJS's don't seem to have a similar feature. Only way to get rid of this hot air is to actually turn on the climate control. Then I'm wondering if Morris is having to extend more energy in cooling extra hot air. Maybe a vent is stuck open somewhere? Because...

If I turn on the climate control and set it to hot, it blows hot air form the proper vents. If I turn on cold air, the cold air comes out of the foot vents, the side vents, and from the defrost, but none from the center panel. I can feel a LITTLE from the center panel, but nothing to write home about. Stuck vent/stuck servo?

And where should I start looking. Morris is coming in for the winter here soon, so I'll have time to look around.

 

Thanks Doug Dwyer, some good tips for me to go on. Much Appreciated!

 

I can't remember if the system is designed to 100% stop all air flow when the system is "off". I wanna say "no, it isn't" but I'm not sure. I'll try to research. Or maybe someone with a better memory will chime in.

However, if it the design allows some airflow I have to think it should be ambient temp, not heated.




Good



[quote]If I turn on cold air, the cold air comes out of the foot vents, the side vents, and from the defrost, but none from the center panel. I can feel a LITTLE from the center panel, but nothing to write home about. Stuck vent/stuck servo?/quote]


That's what it sounds like, yes.




I've fixed two of these Mark III systems (both with erratic operation; exact symptoms forgotten) by unplugging and cleaning the connections and grounds under the dash. There are several connectors on either side of the main climate control case/unit, easily identifiable by their tiny size. A couple are very hard to reach, on the left side, well up there towards to top of the case.

The main grounds are on the two vertical dashboard support braces next to the case. You'll see 'em.

On the two cars I fixed the pins in the connector were covered with green corrosion and the grounds were very rusty.

There are many other checks and possibilities but you gotta make sure all the connections are good before anything else....and there's a chance that cleaning 'em will solve the problem outright.

Note that your Delanair Mark III system has a very different operating scheme than the Mark II system found in the '86 car mentioned in the first posting so fixes/suggestions that apply to one system might not apply to the other

Cheers
DD

 

So next question is: how do I remove the climate control dash panel? This area is new to me on Jaguars, as American cars, being what they are, often just have visible screws you can remove. I see no such simplicity on the XJS!

And, if possible, pictures would be good. I'd hate to start pulling things out/apart, only to realize that I broke something.

 

Not the control panel! Leave that alone for right now.

Remove the left and right under-dash trim panels, and the left and right console "cheek" panels, to gain access to the wiring---or 95% of it.

The under-dash panels are held in with a few screws each, all easily visible. The cheek panels are held in place by the two screws that hold the little vent grilles in place. Remove the screws then wiggle the cheek panels forward.

Cheers
DD