XJ 40 Cabin heater not working.

[Sovereign40L]

Hi Everyone,

My cabin heater has stopped working on my 1990 Sovereign 4.0L. It was sort of providing some heat, but now it's stopped altogether. I had put a cleaning agent in the water system, which did improve the level of heat initially, but now it's stone cold. I was wondering if there may be a water valve in the system, such as the S-type has.

Also, the centre console heating/air con controls, which had occasionally not worked, now work very rarely, so the fans don't even switch on most of the time. The system either doesn't power up at all, or does light up, but then doesn't bring the fans on-line.

I'm assuming that changing the centre console unit will fix the electrical problem. Is this right, and might it also fix the heater problem?

Thanks for any help.

Marcus.

[robv12]

did I read on another post that you had solved this problem??, if not let me know and i'll give you a few suggestion

[Sovereign40L]

Hi Rob,

Thanks for your reply. The current status is that I have changed the climate computer, which appears to work and open vents etc. The passenger side fan is broken and has been removed (just looking for a replacement), but the driver's side fan started working with the new computer.

The remaining problem is that there is still no heat coming through, just cold air. The pipes on either side of the matrix are hot, but we've not checked the matrix itself yet. So, any suggestions would still be most appreciated.

Regards,

Marcus.

[robv12]

if the hot water valve near the bulkhead is opening and closing, which it sounds as though it is, it points the matrix being blocked, you could try a good old rad flush through the sytem and see if that works

[Sovereign40L]

Thanks Rob.

I think we will check the valve first, just to be sure, as I have had a Forte flush in there for weeks. If the valve is working, then I think it will mean a new matrix.

By the way, I know you sell parts on Ebay. Do you have any good condition passenger side cabin fans at the moment? Also, if I do need a valve or matrix, would you have those too?

Regards,

Marcus.

[DEREK1951]

Before you go blaming the matrix you should check that the hot water valve is working , i'm not sure whether your model has one , not all early models did , on later models they started fitting them again .

They are easy to identify on older cars as they're not buried under the inlet manifold as on later cars , they usually fail in the open position but due to limescale it might have just jammed in any position , more likely is your climate control blend flaps are stuck in the full cold position .

First thing to check is to make sure all the vacuum tubes are connected , you might get lucky and find one has come adrift , sometimes a bit of judicious tapping of the blend flap servo motors while operating the heating controls can free up a sticking flap , if not they have to be removed and freed by hand .

Currently i am trying to restore my system on my '93 , so far i've replaced both blowers which has made the car nice and warm this winter , but i've also got a failed hot water valve which although nice now will mean i'm baked come the summer so i'm hoping to change it this year .

They are still available new at jdht , i've also got a center vent problem i'm hoping a replacement ECU will cure but these hvac systems are very difficult to diagnose and being no expert i'm just working my way through the problems bit by bit .

Derek..

[Sovereign40L]

Thanks Derek.

I'm actually going to change the thermostat first, as the pipes are cold on either side of the hot water valve, but I will keep your suggestions in mind if that doesn't bring it up to full heat.

Cheers,

Marcus.

[DEREK1951]

I assumed your thermostat was working correctly , if it isn't , i've had one stick open myself the heater will only just warm up but as soon as you drive off it will quickly cool down and your whole journey will be freezing !

Derek..