After almost a year of restoration, my 1988 XJS12 is finally working. It drives fabulously and even the airco works great. BUT.... I can't get the heater to work. The temperature button on the left gives the same cold air at all indicated temperatures. The little blue to red slide on the bottom does not make a difference. The heater/airco fan on the left only works with the airco on. As fall is coming, I guess I can turn the airco off, but I like to be able to combine heating with cooling to deal with fog in winter.
Do I do something wrong? Do I have a heater problem?
Thanks for the advice.
Cheers,
Daan

 

A couple possibilities for consideration and discussion...just to get things rolling.

Heater valve inoperative. Make sure the little vacuum hose is attached; the default setting is no vacuum = closed valve = no heat. If the hose is attached have a helper slowly operate the temp control dial while you watch the actuator arm on the heater valve. Does it move?

Clogged heater core. Somewhat common. Usually can be flushed clear with a garden hose

Air pocket in heater core. Cooling system needs to be bled.

Call up max heat on the temp control dial. Does the airflow change change to (mostly) the floor vents? It should and, if it does, it tells us the the system understands you want heat and is trying to comply with the request.

These systems are tricky. Sometimes there is a stack-up of faults.

BTW, that little slide lever is to slightly alter the air temp coming out of the dashboard outlets versus lower outlets. It's a subtle thing and you'll feel a difference only when the system has stabilized in blend mode.

Cheers
DD

 

Actually, the heater valve is OPEN with no vacuum. It MIGHT have stuck in the closed position, but normal failure mode is failure open. But still a good idea to see if it will close when vacuum is applied.
Jon

 

Right ! I misspoke. Thanks for catching that!

Cheers
DD