1996 XJS, 4.0 AJ16 , I am not getting any heat from the car. The blower works, demister work,AC works, except the heat. No water inside of car. Where should I start ?? What are the possible problems ??

Thanks

 

I would start at the heater tap, Does it have vacuum, vacuum solenoid is underneath the AC box inside the car behind the LH centre console panel, it should be the front solenoid.

Water tap is located on the firewall behind the engine, it is not uncommon for these to jam. I replaced mine with one from a GM Commodore 8 years ago and it's still going

 

Thanks, I will get on it and keep you posted

 

Not to hijack the thread but interested in knowing if the heat control (vac operated solenoid behind engine) is designed to be on all the time letting water through the heater core when "heat" is called for or in heat mode (not in AC mode). In other words in heat mode, should I expect to see the valve open all the time where the temp switch actually modulates the heat outlet door behind the dash to regulator temperature in the cabin rather than modulate the heater valve of water..
If that is the way it is supposed to work, I would expect the valve to close fully in AC mode to close off hot water to the heater core.

or..
..Like some cars, the heater control modulates the vacuum to the heater control valve for a specified heat setting.
Thanks

 

For the V12 the heater valve is placed as Warren describes: in the top middle at the firewall. At least from cold the coolant loop to the heater is open for flow, as there is a thermal switch in the loop preventing the heating to turn on fans until the coolant has reached a certain temperature.
The heater valve has a vacuum connection and is as far as I remember normally open, i.e. it will close when vacuum is applied.

I don't know if the 6-cylinder cars works in similar way to V12, but I would guess so ?

If you can locate the heater valve: Feel if hoses get warm (if yes: you have flow) and try manipulating the rod pointing downwards. It could just be jammed in closed position

I had a somewhat similar situation when I got mine: Climate control was not reacting to inputs, so I had constant full cooling and either fans off or full fan speed at all settings. A new controller and resoldering a few hair wires in relays and resistor packs solved my issues, but my car has the old Delanair 2 and not the Delanair 3 used in later cars.

 

I'm not 100% sure about late cars such as yours but from the 70s to at least the early 90s the heater valve was intended to be open at all times except when maximum cooling was called for....as evidenced by air coming thru the center dashboard outlet. The a/c compressor was engaged in all modes; all incoming air was refrigerated first and then heated as needed.

But I know the system was revised at some point to allow more/different modes.

Cheers
DD

 

The AJ16 will have an extra small water pump that pumps the water/heat inside the cabin, the usual fault with these is the motor brushes end and the pump stops, everything else normally works. Remove the pump(its under plastic intake elbow), replace the brushes(you'll find them on eBay) and it should be back to normal, just did mine recently. If you hit the pump few times it might temporarily start to work but generally only way to fix it is to remove the motor pump.

 

I used to have a 95 BMW 525 with M50 engine. It also had a small circulating water pump specifically for the heater core because the core sat much higher than the rest of the system. I figured that was why it was cold in the winter.
My Jag is actually warm and very warm when defrost mode is selected. I believe that mode (full clockwise on the fan position) opens full hot and defrost vents with full fan. Temp regulation seems to work but just didn't know if turning the temp control knob actually regulated vacuum to the heater valve to regulate flow or if the knob controlled a heat door with heat valve open all the time , except for AC mode. If it is supposed to be open all the time, then why have a valve at all or why have a vacuum hose to it. So it must open and close at some selection through the controller.

 

The heater valve is normally open and closes with vacuum.

 

ok. When does it close?

 

Delanair mk3 when the is AC on full cold only, other models I'm not sure.

 

Would that be when the temp knob is turned to the coldest position regardless of whether the AC is functioning or not? My AC is not workkng at the moment. Maybe the heat valve closes when I select the AC button. Again, I wonder if just the button function would close the heat valve.
Also, most cars when you select AC, the condenser fan turns on. If the system were low on freon and compressor didst turn on, would the condenser fan still turn on as a function of the AC select switch?
It was mentioned that this is a Delanair Mk III system. Can anyone confirm that this is the latest system and fitted also to the 95 MY models? Or is there a newer type system for facelift cars up to 96?