Heater not working

Hi Dave, thanks for the response.
I could not work out what the normal levels of donations are!

I removed the Motorized in-car aspirator and tested it, the small fan runs and the termistor's resistance changes when you warm it.

When running the engine with the aspirator removed it seems to operate as normal but perhaps not as good at regulating the temp, as you would expect.

With the engine running (and warm) I tried cooling and heating the aspirator's termistor and the system reacted to that as expected. Also I did not see the failure having waiting 30 mins but perhaps it does not show with the car stationary or perhaps I did not quite leave it long enough.

So I'm thinking that's not the problem.

I re-ran the inbuilt diagnostics, at first you get code 0 (no error) and the fan them starts to speed up (sometimes to full speed during the diagnostic cycles) and after 20-30 seconds I get one error code, then after another 10 seconds another and then sometimes a third. These are all active as they have bleeps.

When I reapeat the diags I get the same sequence except the error codes have some differences;

Try 1
Code 0 then after 30 sec code 14, then code 43, then code 46. 14, 43 & 46 then cycle.
Try 2
Code 0 then after 30 sec code 43, then code 45. 43 and 46 then cycle.
Try3
Code 0 then after 30 sec code 43, then code 45
Try 4
Code 0 then after 30 sec code 14, then code 44

I tried the actuactor test sequence (20-27) but that did not change anything.

After a few diag cycles the errors were;
43(Cool Air By-Pass Servo Motor, 11 times)
34(Defrost Vent Feedback Potentiometer, once)
14 (? Twice)
44(Defrost Servo Motor, twice)
45(Defrost Vent Feedback Potentiometer, once)
46(Foot Servo Motor, once)

I keep thinking back to the sound when I get a failure, which is like the center servo motor running but the A/CCM not reading the flap potentiometer correctly and it keeps driving the servo and the gears just click over at their end stop. But if that was the case I assume that I would see a 'Center Vent Feedback Potentiometer' failure code. I am assuming that Jag designed the system so that the flaps would not hit the end stops and then keep clicking!

However your answer seemed to fit well.

If you were working in this car what would you try or do next?

Many thanks.

Many Thanks

I'll book it in an see what the PDU says.

Hi Dave

I had the car checked with a PDU and it threw up codes;

B1268
B1264
B1263
B1266
B1267

Which all seem to be flap feedback potentiometers.

The garage want to change the control unit and all the servo/flaps which I think will be expensive and not the right solution.

I have seen that when you get one error (from the panel diagnostics) then some time later you tend to get a lot more errors.

I suspect that either the cool air bypass flap servo or it's potentiometer or maybe the physical flap is catching somehwere.

Other than that I suppose it could a problem with a common power supply for all the potentiometers which is failing after a period of time or when warm etc.

Anyway thanks for your help.

I did get hold of a. Pdf copy of "SERVICE TRAINING COURSE 703 JAGUAR CLIMATE CONTROL SYSTEMS" which helped explain the system, but not my particular fault.

Did you ever fix this problem? I am have the same problem and can not fix it.

Good day. Okay the car is a 2000 Jaguar XJ8 base 4.0l with single climate control. The problem is the HVAC will blow cold after driving for about 30 minutes. When this happens, you can change anything on the controls and it will not make a different. If you pull over shut the car off wait 5 min start the car the heat will come back sometimes. Now this is the odd part it will only do this if the temp outside is below
0 deg C. Any time it is above 0 all work great.
Also, there are no error codes in the HVAC
I have replaced the heat pump and heater control valve (engine compartment) with brand new units.
New thermostat flushed the system. Back flushed heater core. Pulled out the Aspirator checked it and it works fine. So, the only thing left to do is pull the hot-cold blend door vent servo motor but I can not find were it is one tag said it is on passenger side floor easy to remove but its not there. On another tag it said driver side behind dash cluster. But there is no way to take it out sheet metal for dash in the way.
If this is the right one not sure.

Okay, here is what I am going to do: I am going to hook up a small light 12 volt to the pump yellow and black wire and feed the wires and light out side the hood at the base of the windshield. The light should stay on as long as the pump has power. As my wife drives if the air gets cold the light should go out and then I would know that the wires or the relay are my problem. I need to do it this way because it never gets cold running the engine in the driveway and you can never know when its going to happen. I will all so try the scan tool I have one that stores all data for 4 hour and then I can look at it on the computer.
I will get back to you after I try this idea. Thank you.

Good day, so I hooked up the light and by luck the wife went for a drive and you guessed it the temperature went cold but the light stayed on. So that tells me it's not the pump or the wiring to it. So I though I would play with the heater control value. Started the car all heated up and I unplugged the value it did get colder but I think it went to its default temperature which is 77 degrees not as cold as when your driving but maybe you need the wind to cool it down more. But what I found interesting was if you plug the value back in with the car still running the temperature will stay cold until you shut the car off and let the HVAC reset. Just like when your out driving. This is the closes I have come to reproducing this problem. So I am now going to pull off the value and have a look at it. Do you know does the value work on 12 volts?