Hi all just have a 1997 3.2 x300. The problem is as follows. If I have the heating set to HI and fans on fall I have lovely hot air coming out the foot vents but if I hit the auto button this nice hot air cools a little and if I now select AC but in manual mode I lose all heat. So I found a check to do to tell me if the heater pump is working and that was to put the fans on full and turn the temperature up to HI and check the foot well vents and I get plenty of heat so I’m guessing that means the electric heater pump is working and the heater matrix is ok?

now when I also change from the foot well to the window vent or any other vent setting the airflow does change but I loose heat again.
any ideas on this one?

 

so it seems your heater is working. as you get hot air coming out.
auto will change the temp of the air based on what it thinks the interior temp of your car is.
so is likely never going to be max heat.

when you turn the A/C on of course the air cools down.
yes the ac can operate cold to warmer air. but it is not a reverse cycle A/C.
the ac being on release cold air into the car.
if you put on max temp and put ac on the air will only ever be warm at best.

 

There is a control panel test to give climate control codes you can do easily in this video someone made

There are a couple things this test does not see

 

Here is the Diag PDF to support that

 

See also page 110 and before on the XJ section

T703 BOOK (jagrepair.com)

Look for code 35 as the center vent thumbwheel control , be careful if you pull straight out the center vent box from the cabin as just clipped in as can break the old louvers , patients

There is a cabin temp sensor you can clean below the steering column as a 1 inch square sensor vent , but you have to get at it from the cars fwd , use no solvent , just air and a brush

 

This is your cabin temp sensor as it clogs with lint and again no solvent least dries bearing out

This gets you Max cooling as not biasing the system with bad reading

I have other pics of things somewhere on broke computer

This is a right hand steering of a later X308 model , same system


jaguar-vent-jpg.64591 (4032×3024) (jaguarforum.com)

 

thanks for the reply. Silly me was thinking that if I had AC of and selected 28°c on the control panel that I would get 28°c out and the same if AC was on and I had 28°c selected I work get conditioned air coming out at 28°c. So if I have this correct you are saying that if I have the AC on, the degrees displayed on the control panel will not produce the same temperature coming out so 20°c set on the panel will not produce 20°c air coming out the vent ?

 

I will be trying this out on Monday when I’m next in the car 👍🏻

 

" the degrees displayed on the control panel will not produce the same temperature coming out so 20°c set on the panel will not produce 20°c air coming out the vent ? "



I think the degrees on the panel is the target the cabin temp sensor wants to be and how it gets there changing your vent output temp or cycling the compressor on and off

The heat side does modulate full open / full closed cycles a coolant / heat hose valve , heat fluid electric pump runs all the time

This is where cleaning the sensor becomes important and the lent bias does not show a code , The sensor is feed energy to function as a solid state thermistor and does not dissipate by low airflow making it read hotter than airflow ( equilibrium )

 

the air will never come out at the temp selected regardless.
the temperature is the set point the system is trying to achieve the car to be.
ie, if you set it to 28 degrees it wants to make the car 28 degrees so if it is 20 degrees in the car, it will blow hot/warm until it reaches 28 degrees.
the closer it gets to 28 the air will cool down.

as soon as the A/C compressor is engaged the air will always be cooler than if it is not.
28 degrees with A/C on will be warmer than 20 with A/C on but no where near as warm as even 25 with A/C off.

think of it like this.
the heater is blowing hot air in that is heated by the coolant temp.
A/C compressor activates and refrigerant is used to cool and dehumidify the air.