I have a catch 22 situation on my xjr

It seems that the auxiliary heater pump is on all the time

Right now to survive the heat wave, I unplugged the pump so that the AC can do its job effectively

But eventually I will need heat so I would like the pump to operate efficiently (the heat function works fine if I plug the pump back in but the AC blows lukewarm air…blows ice cold when I unplug the pump)

Any ideas what may cause this and how do I go about rectifying the situation?

My ambient sensor (located in the right brake duct) is throwing an error. Other than that no known issues

thank you

 

Editing in the morning

The ambient air temp sensor is in a bad environment and can be cleaned by removing and installing several times before spraying it

There is a phenomenon that others have observed at high engine RPMs to give you heat , this when they had a non - running pump

There is a water solinoid that should be closed

They put a check valve in the hoses on the later 98 X308 even though they are pretty much the same system

 

Thank you for your reply

I will clean the ambient sensor and see how that goes

I checked that fuse in the diagram. It was a 10 amp one instead of 15 amp. I checked the manual and saw that they also have a 15 amp one. So I replaced it. Didn't change a thing

I read through the section about climate control in the service manual:


It seems that unplugging the pump works bc the flow valve is stuck open. So heat it always at the highest temp and therefore making the AC less effective. But if I unplug the pump, the coolant does not circulate through the heater core. And the AC gets to do its job properly. The troubleshooting section in the manual seems to be in agreement with my hypothesis

I have searched for a fuse for this valve but I can not find it. Help?

(also do you make these electrical diagrams yourself? I have often come across your posts with those diagrams and they are super helpful... I know have the electrical manual and it's very dense...or more like, I am too dense to get what I need out of it!)

 

i thought i read somewhere the heater pump was always running.
i only recently repaired mine so have no idea how it is supposed to work.

cold weather here atm so i have not really been able to test the efficacy of the AC since repairing the heater, but i do know there certainly is a difference in the heat provided based on temp selected.

 

I believe you are correct

The valve on mine is stuck open so in effect, the heater is never turned off. The heat from the heater matrix end up making the cold AC air lukewarm

I just need to test my hypothesis…somehow

 

not sure of best and easiest way to test the valve.
remove and bench test will work but that is not the "easiest" i would think as it requires removal

 

G’day Someguy,

The heater pump motor does in fact run all the time, maybe it shuts off when you demand full cold, but it doesn’t matter as the pump impeller coupling is magnetic and it is the heater valve which controls the coolant flow.

The heater valve is powered open so if yours is always open then it is probably jammed or clogged with scale, it should cycle on and off for normal operation. They are easy enough to remove and service which is what I would do.

Cheers,
Jeff.

 

you can test to see if it is getting the signal to close.
the white plug (the one next to the heater pump plug)
grab a test light.
disconnect the plug.
connect a test light,
turn the temp all the way cold.
light should come on indicating power to close the valve.
turn it to hot and light should be off indicating no power and valve is open.

this way you can easy check the valve has the signal to open or close or not.

 

You can tap on the valve with a broom handle and see if it closes

From my understanding the motor should only be running with the heat selected

The water valve modulates to maintain the selected cabin temp

You might be getting some free flow with the electric motor not spinning with a open valve

The cabin temp sensor has a history on it being clogged with dust , you should not use a solvent to clean ( drys out the sealed bearings )

 

I did this. No power ever comes to the white plug whether there is heating or cooling or the climate control on or off

I even swapped plugs (white with black) and stuck a stethoscope on the heater pump to hear if it ever comes on. It didn’t when the white plug was plugged into it (again under different situations). But was always on with the black

So I can’t rule out that the valve is not working (I can’t hear it turn or off with the black plug)

All I can tell so far is that there is never power to the white plug. I would check the fuse but it seems like it does not have one?

 

Cabin sensor? I assume you mean the ambient sensor in the brake duct?

 

It is always on. From the conclusion of my test

 

G’day to you too

First I need to test of the valve is getting power at all…

 

The valve can be stuck open with..........no powers present

 

Update: I checked the heat flow valve by connecting an external power supply. I can hear it click on and off

So that likely works

it just isn’t getting any power from the AC control module. Hmm. The plot thickens …

 

The valve works. I used the power supply and ran the climate control systems. AC gets cold when the valve is powered and lukewarm when the power to the valve is removed

The only thing that is out is the ambient temp sensor. I find it hard to believe that that would affect any control on the valve’s operation but I could be wrong…

 

There is a control thumbwheel on the center vent

It pops out by the whole vent but you have to be careful if the louvers are brittle



This control thumbwheel is not included on the later V8 X308 which this Doc was made for , but I think it will give you a code on the X300

See page 110

T703 BOOK (jagrepair.com)

and

14-10 (jagrepair.com)

and

 

I did do that check. And the only code I got was for for ambient sensor (code 12)

I cleaned that sensor and the connector itself. Alas! Still throws a code (even after clearing it) and shows “- -“ on the display

The potentiometer in the diagram is just for splitting some of the warm air into those vents so that you can have relatively warmer air (relative to the air at your feet)

 

if the valve is not getting a signal to control the temp then there inlies your problem.
yes the valve may also still be working but it is irrelevant if it is not getting power.
so yes it still may be worth cleaning and testing the valve but obviously need to find the why it is not getting power. (read down and saw you have already tested and seen working)

suggestion number 1 is climate control module.
there is no fuse for the valve as it gets its power direct from the climate control module.
so can only think that it is the control module at fault here.

it would be entirely possible although not really a proper solution to bypass the the climate control module and wire in the heater control valve direct to ACC power with a voltage regulator switch so you can manually control the voltage supplied to open and close as needed.
as i said not a solution and would be annoying, but just a theoretical possibility

 

not sure what can be done in regards to potentially cleaning the sensor, but double check the wiring on it.
it is possible that down near the sensor the wiring has been nicked/split.
when i got my car the sensor was missing. i had err 12 and '--' i purchased a 2nd hand sensor and plugged it in and all good.
at the time i had no sensor my heater pump was not working so i could not get full heat but, my air con did work to get the car cold and there was a difference when the temp was changed. so a missing/broken ambient temp sensor should in no way stop the valve opening and closing.
it should only potentially affect the auto mode (maybe not even)