Hello from a newbie. First of all, thank you to Graham & Rob for helping me on the first posting!

I was driving my wife's XK8, and the hot air heat seems to be stuck "full on". If I switch on the AC, it goes from hot as hell, to mildly hot. It seems as if a damper or some control mechanism is not stopping the flow of hot water to the heater radiator?

Where is a good place to start? For now, can I simply interrupt the water supply line to the heater, so she can drive it without being half naked?

Thanks in advance, and cheers from Washigton State.

Steve

 

I have seen a procedure here for pulling codes and running self tests on the climate control.
Do a,search, or pm me an email and I can send you the XJ8 procedure in the hopes that it is the same.

 

Here is the procedure for pulling the codes with their definition.

 

No



Don't interfere with the supply line or the wardrobe until you've pulled the codes.

Graham

 

Sorry, but I cannot seem to open the Adobe link. Nothing happens.
Thank you for the attempt, though.
Steve

 

You need to have 3 days and 10 posts for full access. Welcome some other new members in the New member section and you can quiclkly get your post count up.

You can also contact me from my website below and I will email it to you.

 

I didn't see a resolution to this thread however my symptoms are pretty much the same.

It started today, driving along and all of a sudden the heat comes on full blast. Understand I'm in Tucson and the outside temp today is in the low 60s F, full blast heat is not required. Apologies to the rest of you freezing folk BTW.

With the climate control in automatic I can run the desired temp down and odd things happen. The blower level increases and it seems to get hotter. Finally the display reads "LO" and we're still hot but not as much.

I got home and ran the system diagnostics which revealed no error codes either current or stored.

I then ran the actuator check procedure. That was interesting. Seems all the outlets and blower levels are working ok but the heat doesn't seem to cycle on and off.

Codes (to me they should be called test modes, but anyway ...) 20, 21 and 22 indicated a water valve is closed, I think that means HEAT. I got heat.

Codes 23 and 24 have a 3 seconds on, 3 seconds off cycle for the water valve with the A/C on simultaneously. I could detect no temperature variation.

Codes 25,26 and 27 all have the water valve open with the A/C on. There was detectable hot air mixed with the cold air from the A/C.

Each code was exercised for at least a minute to be sure I wasn't experiencing residual warmth from the heater core.

Finally, I took the system out of test mode and ran it in manual mode. Running up the fan with the A/C on and setting the desired temp as low as it could go still produced hot air mixed with the cold air from the A/C.

I'm thinking this "water valve" or its controlling circuitry is the issue.

Can someone point me further in tracing the fault? Is there a specific fuse I can check? Just where is this valve anyway? With my luck it probably requires motor removal.

Thanks in advance!
Scott

 

I have no experience with this but your diagnosis make sense. Perhaps this pdf can start you on you search. Maybe the connector on item 3 needs cleaning.

 

That's a great help, many thanks. It also looks like I can get at the stuff easily (well, I suppose that's a relative term, this is a Jaguar) without much fuss.

 

Turns out it was a dirty electrical connection.

As the documents you provided indicate, with no signal to the water valve, the hot water is run through the heater matrix, leaving it on all the time.

The connector going directly into the water valve was not the problem however there is one just a couple of inches further "downstream". When I cleaned it, things started working again.

Of note for future reference: The signal from the ACCM which controls the water valve seems to go from +14V to disrupt the hot coolant (jumbo shrimp?) flow to and from the heater matrix to +7V which allows the hot coolant into the matrix. I had expected it to drop to zero volts but heck, it's working now.

Also of note: The documentation indicates there's a pulse mode in one of the test modes/codes which should be 3 seconds on and 3 seconds off. I noted about 5 seconds on and 1 second off. Now this documentation is for a 1998 and I've got a 1999 so not sure if that's significant. It could also be the test mode cycles variably as normal operation pulses the valve at different rates depending on the heat demand.


Thanks again for the help. This forum is awesome!

 

Glad it worked out for you. Sometimes big problems can have simple solutions.

 

1/27/16, a quick update. This thread was pertaining to my wife's XK8. My 1999 VDP, decided to do the opposite. The heat died. I took a hammer and smacked the aux water pump. Instant heat! That lasted 3 days. After seeing the replacement cost, I investigated an alternative. I ended up using A Bosch water pump from a VW Jetta. It was $68.00, instead of the $520.00 from Jaguar. I adapted it and all was well - for a week. Now I'm thinking the car is out to get me. I determined there was no coolant coming into the "input side" of the pump. I then jumped out the 2 "bottom" hoses on the heater water valve, and presto, heat. Massive amounts of it. I can roast a turkey in the car now. I plan on installing a brass gate valve used on Pex pipe, and manually control the flow that way. Lowe's has the 3/4" valve for $9.00. I wanted anyone reading this to know there is always a solution to every problem. Live long & prosper.