Series III XJ6 No heat

Keep in mind this is a clapped out $400 XJ6 The celebrity of my latest posts.

  • There is coolant.
  • The engine thermostat is working checked with an IR thermometer.
  • The (heater) blowers do come on at any setting other than low
  • I don’t believe the internal temp switch is working - I don’t here it click on or off; but then again there isn’t any reason for it to click off or on because there just ambient air coming through the vents. :wink:
  • The A/C doesn’t work. - I think this goes way beyond needing to be recharged. Not real high on my list right now. I know it’s required in order for the climate control to function properly.
  • is the slider under the climate control the “by pass”? I don’t think it works either. It’s got a pretty stiff detent when sliding back and forth.

Temperature control valve? I’m guessing.
Funds for this car are limited. I see AC Delco has a unit but it’s plastic but it’s also only $15.00US or I can get the metal OE replacement for somewhere between $50 and $75US. Has anyone used the plastic one? Successes or failures?

I see there’s another unfortunate that is experiencing the same issue. I’m following that thread too. So, I guess this post is rather pointless.

Quick fix heater control valve? thoughts?



Can you determine if the hot water valve is opening or not…do the heater pipes inside the car ever warm up? I think the plastic valve is fine. You could have a number of things going on with your climate control…and previous owners can do many interesting things to a single function to work.

If you select 65 then wait a moment and then select 85, do you hear or see the servo flap rods moving? ( located behind right cheek panel).

Do you have vacuum at the hot water valve? Vacuum closes the valve…cut the vacuum and it should open…could be bad.

Cold water temp sensor can be bypassed by disconnecting and jumping connection.

Check that first…then we can move on.



I used the plastic delco one on my series two years ago. It was still working fine when the car was finally parked. The plastic one does not mount the same as the original but the hoses work fin3 to keep it in position.

Thank you Geoff, I appreciate the feedback.

Sent from my BlackBerry 10 smartphone on the Verizon Wireless 4G LTE network.

the only heat is from the engine radiating through the bulkhead. the air is pretty much ambient. I’m quite sure there’s something going on with the climate control. The car is a clapped out POS. but It’s a Jag.
I haven’t checked the valving yet or vacuum for that matter.

I will listen. for the flap. The '85 air works perfectly. so I know exactly what you’re on about.
I will report back tomorrow morning. It’s 9pm here Thursday; and it’s dark.

I’m heading out to the garage to figure out how to get the bearings, seals, and spacers out of the IRS Hub.

I’ll report back tomorrow AM
Thank you :slight_smile:

I have the plastic valve in my car, it’s been more than ten years now and still works fine.
Highly recommended.
It has no support brackets though, but you don’t really need them, it’s very light and the hose is stiff enough to keep it in place.


There are three factors involved, Mark…

The heater valve is open (coolant circulating) with no vacuum at the valve. The valve may be mechanically stuck - or vacuum is applied by the servo because the servo is in full cold. An AC amp problem? Disconnect vacuum hose and check for heat - a faulty valve is best replaced…

Heating is provided by changing flap setting to divert air through the heater core - which should be hot. Coolant circulation through core is usually checked by verifying that both hoses at the core are hot…

If the servo does not reset flaps, air will not be heated. Check servo movement…

xj6 85 Sov Europe (UK/NZ)

I have a similar but different problem. When I start the car in the morning, the heat comes on and blows hot. It comes out of both the bottom and face vents and, as Gary has suggested, I probably have a vacuum issue, which I plan to try to track down. But the different problem I want to share is after I park the car for an hour or so and drive it again, I can’t get the heat to come back. The air blows cold even if the right knob is set at 85. So like Mark, I’m thinking my issue may be the internal temp sensor as well. Is it hard to replace? I don’t even know where it is.

The heater control valve is mounted on the bulkhead directly behind the center of the engine. On a XK6 it’s not too bad to get to, on a V12, as you can imagine It’s a bit tougher.

Thanks, Mark. I actually replaced the heater control valve a month or so ago. But I think the temperature sensor in my interior is defective. I don’t know where that is. That’s what I’m assuming is wrong anyway.

The sensor for cabin temperature is located right beneath the crash roll (dash top) about in the middle of the car. You need to remove the screws holding the crash roll in place, and slide the crash roll rearward to access it.

I have been on Jag-Lovers for about 18 years now and I don’t ever remember anyone posting about a failed temperature sensor. It is probably a good idea to inspect it visually to make sure it is present and the two wires are connected but I suspect that it is not the cause of your climate control problems.

In that same 18 years I have seen dozens (hundreds?) of Delanair II climate control system problems caused by failed OEM A/C amplifiers. I have even experienced a few myself where all of a sudden the climate control gets stuck in either heat or cold, or seems to have a mind of it’s own.

In my opinion there are only two kinds of OEM A/C amplifiers, ones that have failed and ones that will fail.

I recently posted about the five kinds of A/C amplifiers that I have found in my two Series III XJ6 VdPs, the three Series III XJ6 parts cars I have purchased, and ones that I have purchased online. In addition to the brown OEM units (which I would consider guilty unless proven innocent), there were two aftermarket white shotgun shell shaped unit’s (from Australia?), a grey brick shaped aftermarket unit, and a new unit that I purchased recently. Of about 10 OEM units that I have had, only 1 is still working yet all the aftermarket units worked when I recently tested them.

I suspect that your problem is a failed A/C amplifier and the only way to fix it is with a replacement A/C amplifier. There are lots of posts in the Jag-Lovers archives about flaky or inoperative climate control problems and some recent threads about how to verify that and options available to resolve you problem.


Status update on the “No-Heat”
well I guess I’m mistaken I think the thermostat is stuck open cause it doesn’t get hot. it hovers around 70c. If there’s suction it’s very little. the hose is too short, and I’m not long enough to get my head in there and stick my tongue on it. :laughing: Isn’t that how everybody checks vacuum?

I purchased a Mityvac hand pump years ago at a local auto parts store and use it regularly on a variety of car projects to drain fluids and check vacuum.


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Thank you for the input. I should have mentioned I just replaced my amplifier. That’s why I thought the problem must be my interior temp sensor. But if those almost never fail then I doubt that’s the problem. Now I wonder if my mechanic dialed in the amplifier incorrectly. He said he followed the steps but now I’m not so sure.

I hope I haven’t hijacked this post. My problem seems similar enough to Mark’s so that’s why I posted.

It’s so bizarre my heater works great on the first drive in the morning but becomes really cold on the second and subsequent drives during the day. :-/


General vacuum is an ‘easy’ and necessary check, Danny - the system require vacuum to perform. A vacuum gauge is required - which is a recommended useful instrument anyway…

One quick-test; the defrost vents is held closed by vacuum - and should be closed in al switch positions, except ‘def’. The centre vents are indeed opened by vacuum, as directed by the servo in ‘cool’ mode. If the defrosters stay closed as they should, and the centre vents open; there is vacuum to the system - and it is a control problem…

As Paul says; the in-car sensor seldom fails - and a faulty AC amp is a likely cause. Have you checked if the servo moves as temp is alternately set to ‘65’ and ‘85’…:slight_smile:

The standard AC amp is a ‘plug and play’ device - there is no need to ‘dial in’; ask the mechanic to clarify. However, there are two different versions, with slightly different wiring - and there is also an in-line 1A fuse to be checked…

The ‘heat in the morning’, but not later, is odd - but may simply be an erratic AC amp; a typical AC amp fault is indeed that it arbitrarily resets servo. A faulty in-car sensor cannot conceivably do this… :slight_smile:

xj6 85 Sov Europe (UK/NZ)

Even with low coolant temp there should be heating, Mark. Check heater core inlet and outlet hose temps. The ‘in’ hose should show coolant temps - the ‘out’ hose some 10 - 20C lower, indicating that coolant is circulating through the heater. A blocked core gives no/little heat…

The low coolant temp is indeed a sign of a faulty thermostat. Typically; the engine should reach operating/thermostat temp after some 5 min of driving - prolonged warm-up time indicates a thermostat not staying closed during warm-up…

This is a separate problem, but should be remedied. Cool running is not good for the engine - and will of course interfere with heating efficiency…

xj6 85 Sov Europe (UK/NZ)

The defrost vents do work properly. They close when they should and open when defrost is set. The face vents and bottom vents are a different story, however. They both stay open at 65 and at 85. In defrost mode, the bottom vents close but the top, middle vents stay open.

The servo does work and it whirs when I move the temperature setting back and forth. It also whirs when they system decides it needs adjusting.

I got the amp from Jag-Aire a month ago. The amp brought my system back to life. Maybe “dial-in” is the wrong term but the amp comes with instructions to set it up properly. I’m wondering if my mechanic did something wrong though he told me he followed the steps.

Besides the amp, he fixed a vacuum problem, installed a new compressor, a new heater valve, and had to adjust the arms and springs to the Servo. Yes, my system was a mess! It’s obviously better now because it didn’t work at all before but I still have these remaining issues that are frustrating. After the first drive of the day when the heater blows hot, the system then blows so cold while set at 85 that I have to shut it off. :-/

One other question someone may know the answer to - a friend of mine who is sensitive to mold complains he can smell mold in the car from the AC system. I don’t notice it, but I believe him. Someone suggested spraying Lysol in the front air intake with the system running. Has anyone run into this issue?

There’s some progress there Danny!

I suggest you go over it and re-adjust it your self (sorry, I don’t trust mechanics), it’s quite a delicate procedure and it has to be right for the system to work correctly.

The face vents are open in all modes, as they can be closed manually, that’s why they are inscribed with a “Close for Max Defrost”.

The bottom vents however should be closed when the system is in Defrost mode. IIRC, they are controlled by a Vacuum actuator, mounted at the left side of the Delanair box.
Check that it’s free to move, that it sees vacuum when it should and that it moves when you apply vacuum.

Tis about time around here to get heat from the Jaguar as well as the Jeep.

My Jaguar had the plastic valve when I go it. Works just fine. At least most of the time. When the warm is slow in coming, I set the fan to auto or is it defrost? And the temp at 85. That usually brings on nice warm air from the center vent.

And, yes the heat hoses support the plastic valve just fine sans any brackets.

I did add a manual valve to the opposite hose.
I call it my winter/summer valve. With it and the heat valve off, no hot water in the matrix. I can power vent with the fan controls. In mild weather using ambient air…


Thank you, Aristides!

Maybe I misspoke when I said face vents. The center, top vents remain open at 65 and 85. As do the bottom vents. The bottom vents close during defrost but the center, top vents remain open.

Also, I just drove the car this morning. As before, the heat worked well initially. I kept it set at 85. But as the car interior warmed, the air got cooler and cooler and then turned pretty cold. When I turned defrost on, the air turned hot again but got cool again when I set it back to Auto or Low.