Climate Control Air Flow

Trying to figure out my climate control in my 88 XJS. I have removed my A/C, btw.

As I drive, I notice there is no air flow coming through the vents, unless I turn on the fan. So I turn it to LOW. But when I turn it all the way to cold, the low fan speed goes much higher. I have to set it to about 70F to get the fan speed down on low, but then it blows heated air on me.

I have the temp control switch pulled out, which I believe is manual.

Is there a way for simple air flow from outside? Right now, I have to crack the window, or listen to a loud fan.

I know there’s a bottom lever, but not sure what that does.


I think you have the Delanair Mk III system like I do. I have a manual for it that I’m happy to email if you don’t have it/can’t find it. I have been working on my 89’s climate system a bunch recently. A few things I’ve learned that might help you:

  1. the system’s default is to allow coolant through the heater core. If you turn on the A/C (moot point in your case I understand) and the compressor engages (meaning it’s charged enough etc.) then an electric switch enables vacuum on the heater valve. When this valve has vacuum applied it closes thereby blocking the heater core.
  2. all/much of the air that makes it to the cabin flows by/through the heater core meaning that the only way you will ever get ambient air flowing in is if the heater core is blocked off by the valve (and thereby not full of hot coolant)
  3. what you need to do since you pulled the A/C is probably bypass the electric switch such that there is always vacuum pulling on the heater valve. Then again this has the undesired effect of disabling your heat unless you undo the bypass. But maybe this isn’t a big deal to you if you don’t need to go between outside air and heated air too often.
  4. I know nothing about the switch that allows/blocks the vacuum. Probably would be easy enough to control the signal too it some other way (wire it to the temperature selector knob??)

These points from my personal experience. Take with a grain of salt and others who may be more of experts chime in if I’m mistaken on anything!

A big part of how I deduced the above was through the process of unblocking my clogged heater core. When it was clogged before the air coming through when set to cool (my A/C also not work) was outside air temp but once the heater core was not clogged the air coming through was heated. I explained this to myself with the above logic. Hope it helps.

Oh and the bottom lever is only relevant to heat. It is a way for you to preference if the car sends more heat to feet or more to dash vents. I don’t think it does anything when the temperature is not set to heat.

Hope this helps some!

Greg, you need to confirm that. Do you have the Mk II or the Mk III? On the Mk III, the left knob can be pulled out for a manual mode.

I must have Mk3. I can pull out the left knob for manual.

Douglas, thanks for the info. Very confusing Climate Control. Not sure what to do at this point, here in Seattle, I like to either switch to outside air flow (when it’s 60F and up) or heater (when it’s below 60F). Our usual range is 50F-70F :wink:

The climate control system was never intended to operate without an A/C compressor running. Since you have removed it, it’ll probably never be quite right. You’re fortunate in having the manual mode; the Mk II didn’t even have that.

I might suggest you manually block off the flow to the heater core in the summer months.

You might also be able to make some modifications to the system, such as manual control of the flap servos.

Did you remove the evaporator?

Oh, one other thing: If the climate control system cannot maintain the set temperature – which it often won’t be able to on account of there being no A/C – it’ll probably try to close the outdoor vents and switch to recirc mode. You’ll probably want to find a way to override that.

Then what is the manual mode for?! I was hoping I was doing something wrong, but sounds like an uphill battle to sort out. Even with AC, I’d want outdoor air instead to cool off. Most cars allow you to set cool, and then decide if you want ac or not, when in manual mode.

Looks like cracking the window with fan off is the solution for now.

No, I didn’t remove evaporator.

Don’t know how different the Delanair II is from Delanair III system, I have the II, but it sounds like your system is in Auto mode and not in Manual. In Manual mode the fan speed should remain in Low regardless. Maybe something is wrong with your switch ?

Look for the Bernett mode, very easy to do, you can turn the fans On and Off with an external switch, but keeps the fresh air and temp setting active.

Yes, it will most definitely do that… and even when it’s not that hot outside, and with out a AC, it will just recirculate hot air and, en plus, transfer all the heat from the engine inside the cabin.
As I have a manual switch for the AC compressor I ran into this situation many times and I had to switch on the AC even though the air outside was cool enough…
I’ve put a Recirc disable switch and it was a very worthwhile modification.

I remember on some old cars…they would add a regular plumber’s water valve to the heater hose and shut it off in summer

I’ll look into it…but when in manual mode, the fan does stay on low at all temps, unless I put the temp all the way to the coldest setting. Maybe when you do that, it disables manual mode?

I’m getting the feeling this climate system was set up for the driver who wants an exact controlled internal system with no outside air interfering with their comfort. :slight_smile:

So I fooled around with the manual setting a bit this morning, seems I can set it a hair below 70, to I would say 68, and the fan remains on low. As soon as I go below that, I hear a click, and the fan comes on much stronger. So obviously it is overriding manual setting under 68F.

So it looks like I’m stuck with 68F at low fan speed, or cooler at a high fan speed. Too bad, because in the mornings, I love having high 50’s/low 60’s coming thru the vents from the outside. 68F is just too warm for me. I guess I’m not a true Jaguar driver…

Such things are readily available:

Ha! Can’t believe I’d have to do that just to get cool outside air flowing through. But it is a Jaguar…

I’m tempted, I may look into it next year, as summer is almost over here in the NW, so I’ll be using the heater very soon.

But wouldn’t that put extra pressure on the heater hose I attach it to? Would it affect cooling at all?

The heater valve in the car already closes off flow. It just only does it when the climate control sees fit, and that’s only when calling for max cooling. And it’s always open when the car is started because there isn’t any vacuum available yet.

OK, thanks Kirby. I may do that next spring. I’m a Seattle guy, so LOVE low 60s cool damp weather. :slight_smile: