Hello everyone,

I have an issue with my s-type v8 4.0 Jaguar concerning the heating. Maybe someone here with more experience than me might have an idea what it is.

I did a few tests with different settings on the console and here is what i found.

When A/C is turned on, no matter which setting, from low to hi, the air coming out will be cold. So cold air is no problem.

With A/C turned off, the air coming out is always warm, but only lukewarm. The heating performance is very weak and seems to be independent on if i set it to hi or low.
When driving the car, the heating performance is even weaker it seems. Standing still while the motor is running the heating performance is a little better but weak still as mentioned above.



Could this be the heater valve?

But if it was the heater valve, then wouldn't the air coming out be always cold or always very warm, rather than lukewarm as it is now, especially when driving?

Also, why would the A/C when on always produce cold air? Shouldn't if i set it to HI or 29°C the A/C simply stop, given the heater valve is damaged?


This s-type also has an extra electric water pump for the heater. I thought that this one could be damaged as well, explaining why lukewarm air is coming out still, but again, it does not seem to explain why with the A/C on i always get cold air, no matter the temperature setting.

Unfortunately i don't know much about those matters, so maybe my reasoning is flawed.
Hopefully someone can shine some light on this!

 

Check Fuse #1 in the engine bay fuse box.

With engine warm check both metal lines going to the cabin with a laser thermometer. If those temperatures are less than 120 degrees with your heater set to "hi" your DCCV soleniods are stuck closed or partially closed.

Rather common issue.

I wouldn't be concerned about the aux pump at this point as your probably looking at a DCCV swap out.

 

+1 on that. As far as the heater output, the aux coolant pump merely bumps up the coolant flow at low RPM. At cruising speed, the aux pump should be off. So if you're still getting low heat at freeway speeds, it's not the aux coolant pump at fault.

More details, plus a VERY simple troubleshooting method, can be found here:

https://www.jaguarforums.com/forum/s...dition-177764/

 

Thanks, that is an amazing link you gave there.

It seemed impossible to remove the plug on the heater valve without removing a lot of other stuff out of the way first, at least that is what some car mechanic concluded.

With this neat trick, it seems that i won't have to do this at all for some time limited testing purpose(as the engine might overheat otherwise, disabling the aux pump at the same time by pulling the fuse).


However, i cannot really follow the logic of this completely.

If, as the link you provided says, the heater valve got stuck in a closed position, or half closed position, then this is a position it would normally not get stuck at if the heater valve fails.

According to the link, if the heater valve fails, it usually gets stuck in the open position, hence you get too much heat inside the cabin, no matter which temp you set at the console.


What i don't understand is, why the author of the thread you posted the link of, is so confident that the heater valve will unstuck once you pull the plug.
And why he would be so confident that this can but only mean that the heater valve is damaged.

My thinking is, that if the electric control mechanism, controlling the ON/OFF position of this valve is functioning correctly, then when it sends the OFF or ON signal(in the case of wanting to opening the valve, it would send the signal to cut electricity, similar to pulling the plug i would think) which results in the heater valve opening up, then this would be equivalent to pulling the plug.
So if the electric control mechanism is working correctly, and in spite of that the valve is stuck still, i do not see by which logic it would unstuck if you pull the plug.

However, i am no expert and the full details of how the valve and the electric control mechanism work escape me, so i would welcome anyone to enlighten me, when considering the above first.

 

Usually is not always. The wretchedly made things fail in lots of ways, commonly also taking the module out as well

 

I created a rather lengthy thread here on the forum regarding my DCCV experience. Long story short I took apart my failed DCCV and both solenoids were stuck in a 90 - 95% closed position.

Regarding the plug to the DCCV, yes, it's a PITA to get to, hence removing fuse #1 - As long as you're cooling system is in check your car will not overheat due to this fuse bring removed.

Finally, to get to the DCCV plug I find it best to remove the air intake tube and loosen the bolt to the aux cooling pump.

That gives you enough room to get to the plug, clip the red cover up exposing the releasing tab. Depress while you pull up on the plug.

That's my $0.02 on your current issue.

I'm still sticking with either a faulty DCCV (solenoids stuck closed with debris - there's rubber in that unit that deteriorates over time affecting solenoid operation) or a blown fuse (which means your DCCV is on its way out)

 

I wrote that, thanks. I think I see the source of confusion. I wrote:

"I've often recommended disconnecting the electrical connector from the DCCV. This removes any electrical command and the valves SHOULD spring open and give max heat."

I had put "SHOULD" in all caps because that is how a good DCCV will behave. In the previous sentence, I had warned the valves are prone to jamming. If you have a jammed DCCV, it obviously won't spring open. That's what were trying to determine, the ability of the DCCV to respond to input commands. If the DCCV is jammed, it won't change by unplugging it. A good one will, but a jammed one won't.

Did that explain it?

 

Partly. What i do not understand still is, that if the valve would spring open when pulling the plug, given the electrical control mechanism controlling the valve is working properly still, shouldn't then the valve spring open anyway and not get stuck in the first place?

As i imagine it, the electrical control mechanism when attempting to open the valve, would simply do the equivalent of us pulling the plug off of the valve in a sense.

So if the valve does indeed spring open when pulling the plug, if the way i imagine it would be correct, then it would indicate a problem with the electrical control mechanism, rather than a damaged valve.

However, as i said before, i have no clue whatsoever on how this mechanism actually works, so i might be far off.

In any case, i will try your neat trick tomorrow to see if i can get the valve to spring open and will report back about my findings.

 

If it's stuck it's stuck.

Would and should are not the same!

 

The first thing that comes to mind is the warden in Cool Hand Luke: "What we've got here is a failure to communicate."

Pulling that plug doesn't change anything mechanical inside the DCCV. All it does is remove a possible erroneous electrical command (which is not very likely) supplying power to close the internal valves.

When you shut off your engine after every trip, power is also removed from the DCCV. The spring action should (key word) open the valves, assuming they aren't stuck. But since no coolant is flowing with the engine off, you have no way of knowing what the valves are doing.

When you're driving along and request heat, the control circuit removes power to let the DCCV open and flow hot coolant to the heater core. Pulling that connector, or removing the fuse, does the same basic thing. Remember, it doesn't change anything mechanical inside the DCCV. It let's a DCCV in good condition open up. If the hot coolant still doesn't reach the heater core, the DCCV is stuck shut, even with the springs trying to open it.

 

edit: need to rethink

 

I think i understand now.
What you just described is the same as i was imagining it. In particular this part

"When you're driving along and request heat, the control circuit removes power to let the DCCV open and flow hot coolant to the heater core. Pulling that connector, or removing the fuse, does the same basic thing."


So basically, after pulling the plug or fuse with heat set to max:

case1: you get hot air inside the cabin => control circuit is damaged probably or the cables leading to the DCCV are damaged, or both.

case2: the air is colder than expected => heater valve is damaged with the additional possibility of the control circuit being damaged as well.

Is that about right?

 

​​​​​​
Yep, you got it.