Heater

[simondmill504]

Bought car in heat wave so ensured air con works, which it does very well. Never thought to check the heater, until yesterday. Doesn't really work but thought I got the occasional waft of heat, which frankly I would rather not have done, as that would suggest a simple repair like the divert valve unlikely.

Very late 4.0 Celebration, anyone know of obvious culprit before I start the usual trail?

Thanks

Simon

[SimonR]

Hi Simon,

I had this problem in a previous XJ-S, albeit a pre-facelift one. The issue was that the sensor in the Aircon evaporator under the dash had failed so the AC remained on at all times, to the point where it iced up completely.

Do you hear your AC compressor clutch engaging and disengaging? - Or if you pull the fuse for it, do you get heat?

[simondmill504]

Thanks

Air con is switching off and on as it should do but thanks for the thought.

[steve_m]

It could simply be the heater valve on the firewall that is stuck; they can appear to move externally but diddly squat is happening internally.
That's assuming that the 4 litre gubbins is similar to the V12.
Have you tried a back flush through the heater matrix?

Best to try the simple stuff first, before you rip the dashboard out.

[ptjs1]

+1 for checking the heater valve. It's the same type of setup to a v12. Get one person in the car, set controls to aircon on and cold start car, let it warm up. Check input pipe to heater valve is warm. Get someone to change aurcon temp to full hot whilst you watch the valve open and feel for heat on output side of valve.

Good luck

Paul

[simondmill504]

Thanks

Was driving car this morning with heater off so had a look when I got back. With temp set to cold both sides of valve are hot as is the return pipe however no signs of movement when switched control to hot suggesting valve is not changing position however although pipes hot in either position air output stays the same ie cold. I would have expected car to be hot if valve stuck open. Or am I mis-understanding something?