HVAC Temperature control issues
 

So now that it's cold outside I'm starting to think having heat might be beneficial. :icon_cool: So here's where it stands now. I can get hot air, sometimes, but it will only blow hot at low fan speeds. In other words, for example if I have the temp dial all the way hot and the fan on auto it will lightly blow warm air for awhile, then I'll hear some servos moving and all of a sudden it's blasting cold air at full fan speed. Sometimes it will switch back to hot and when it does, fan speed reduces again. From my understanding of the system, which is admittedly limited, this essentially means one of two things. A) The amp for the system is freaking out or B) the interior temp sensor is constantly giving a near full hot reading to the amp, causing it to think there's no need for heat since it's already 140 degrees in here :icon_saywhat:. My question for you guys is, is this something that could be corrected, potentially, by adjusting the amp and if so, what's the procedure to adjust it? I've seen it kicking around these parts before but have searched for hours and can't seem to find it right now. Everything else seems to work fine as far as what vents the air blows out of and such (may only have 2 or 3 fan speeds right now, have to check those relays) but something's off in the temp control. Any information on the location and procedure for checking the temp senders and checking/adjusting the amp would be much appreciated.

There IS an adjustment on the amplifier that you could tweak a bit to see if anything improves. I can't remember the details but I think there's a hole with a tiny screw inside. If you take a close look at the amp you'll probably see it.

Fan speeds:

The #4 (highest) speed will operate only in full cooling mode or defrost mode.

The #1 (lowest) speed will not operate in cooling mode but WILL operate in heating or blending mode.

Cheers
DD

What did the A/C do when the temperature was warmer?

The factory manual has a fairly good diagnostic section on climatete clontrol. You need the patience of a saint to work thru it, especially if you lose track of your steps and acidentally invalidate your work !

Or, treat yourself to :

Jaguar Books & Manuals | Jaguar Parts Manual
(scroll down a bit after the page opens)

There's no way to "check" the amp, really. And many of the tests/diagnositcs won't make much sense without a "known good" amp. It's a catch 22

Cheers
DD

Factory manuals for workshop and parts are excellent, really worth buying, and you're likely to need them with your car as there will no doubt be a few jobs needing doing in the future. These are also real books, not CDs or on-line so you can sit by the fire side and read them if the weather is too cold to do the work !!

Here is a UK site - the manuals are not all that cheap, but there is nothing else with the depth of information.

Classic Jaguar, Jaguar XJ Series 3 Workshop Manual XJ Series 3 6 & 12 CYL. (AKM9006*) | JustJagsUK.com

Classic Jaguar, Jaguar XJ Series 3 Jaguar XJ6 & Daimler Sovereign Series 3 Parts Catalogue (RTC9885CF) | JustJagsUK.com

I have the CD version of the manual (though I seem to have misplaced it at the moment). Are we all fairly in agreement, then, that my issue sounds like an amp or temp sender issue? What am I adjusting when I turn the screw on the amp and which direction adjusts it which way?

Amp issue more likely than sensor issue.

Can't remember which direction to turn adjustment screw, sorry.

Cheers
DD

For anyone else who stumbles across this, procedure for amp adjustment from alldata

1. Set the temperature selector at 75 and run vehicle at 1500 rpm.
2. Ensure engine temperature is normal and ambient temperature is fairly stable.
3. Measure the air temperature in the region of the in-car sensor using a mercury thermometer.
4. When the temperature on the Mercury thermometer has stabilized and the camshaft ceases to move, note the difference in temperature between the 75 selected at the temperature selector and that registered by the Mercury thermometer.
5. Every 5°F between the two items equals 45°angular rotation of the temperature control.
6. If the temperature is higher at the Mercury thermometer than the selected at the temperature selector, rotate the amplifier potentiometer adjusting screw anti-clockwise by the same angular amount as that estimated at the temperature selector.
7. Similarly, if temperature is lower at the Mercury thermometer, adjust in a clockwise direction.

I will give this a go in the next couple days and report back. On a side note, holy mother of God what a ridiculous and unnecessarily complicated system. How I long for dials that pull cables to change temp and airflow location. :icon_confused:

I'd be perfectly happy with manual controls as well.

When working properly the Delaniar MkII is a terrific system.....about the only "automatic climate control" system that I really liked....but they can be a real stinker when problems come up.

Cheers
DD

I agree with Doug, most likely the amp. The reason I asked about how the A/C acted in warmer weather is because my A/C was acting strange right after I got my car ('86 VdP) where the air would work and then it would all of sudden turn to blowing hot air and then might switch back. I replaced the amp on mine (with one from Jagbits I believe) and that cured my ills. A/C has worked great since. I also agree with Doug, annoying when something goes bad, but now that it's working properly, the system works very well.

Good luck,

Eric

Well, played with the adjustment on the amp to no avail still had no heat....until about a week later when it all of a sudden started working and has been working consistently for the last few days. Go figure. I had never had it give more than warm air and only for 5 minutes max before it reverted to cold. Now it blows hot air without ever switching back. I think I've also got an issue with the 3rd and/or 2nd speed relay as it seems like I have a low speed or two and full blast cold but the heat won't blow more than lightly.

I have the opposite problem on a 2004 XKR coupe. In Texas we have a lot of mild weather in the winter. Even when set on a cool temp. like 67-68, the heater blows warm air. Seems like the heater valve is not responding to the temperature setting correctly. Anybody else had this one?

110% different system, check the forum for your car for info on that. As far as mine goes, heat worked for 2 or 3 days then reverted back to no heat. Time for an amp I guess.