2004 XKR Coupe
Once the motor is hot/warm, the heat blows warm air no matter what temp is set on the dash. So the heat is fine from cold start, but once the warm engine is parked for awhile, the heat is on and the only way to get cool air from it is to run the AC. Must be a malfunctioning valve somewhere. 72k miles and this beauty is perfect except for this one issue. Is this a common prob? Thx, Tom

 

Check first for climate error codes using the attached procedure.

A faulty valve may not be detected, however. The heater valve is on the left side engine compartment, at the firewall.

 

Thanks for telling me about the heater diagnostics, WhiteXKR. I didn't know about those. I pulled 3 codes: 23. 43 & 14. I think only 14 is relevant to my issue since the AC blows cold. The 14 fault code refers me to the PDU, not sure what that is. Can anyone interpret?
Thanks, connalrad Black 04 XKR coupe, Miss kitty

 

PDU is the Jaguar portable diagnostic unit so I'm guessing you need a visit to a dealer

 

Tom,

I'm curious to know why you would normally run with the AC off. The Jaguar recommendation is to use AUTO (Automatic Climate Control) as the normal operating mode.

Graham

 

I run the AC only when the weather is hot, guess my thinking is I'm sparing the AC compressor load on the motor, and saving a little gas, thereby putting less carbon in the planet. I never knew Jag says the auto mode is the default mode Graham, how do you understand and do you feel that's true for an older XKR - 2004?

Thanks, Tom and Miss Kitty

 

It is funny, this is probably the only vehicle I've owned that doesn't seem to display any power loss due to the drain from a running ac compressor. I was wondering if you might mention that for a reason.

Guess they just effectively engineer it to cut out when you demand power.

 

I had the same problem with not hot air blowing in my '99. Look at the hot water feed to heater core on driver's side of fire wall. You will see a hose with an impossible short 180 degree bend. Mine was so tight little water got through. It was replaced by a modified hose that allows unrestricted water flow, now all is toasty! It is a PIA to get to!

 

You should follow the instructions to clear the codes and then see which, if any return. Sometimes codes get set during previous servicing and remain in memory until they are cleared.

 

I understand it because I've previously owned that era of XK8 and took the trouble to read the Driver's Handbook:


(click on the image to enlarge it)

See the section boxed in RED.

Graham

 

I've read parts of the manual, just not that section. Thanks for taking the time to enlighten me. I'm going to see how well I like using auto as a default. Maybe should read all the manual too, since there are probably other things I don't understand well. The systems Jaguar built into these cars are amazingly complex.

Tom and Miss Kitty

 

Mine does the same thing. I just turn the heater off entirely and lower the top :-)

I did notice, shortly before I noticed the heat on all the time problem, that there were some bits of foam occasionally blowing out of the vents. I suspect that there's some door deep in the heater system that had a foam seal around it which has now decomposed and is letting hot air through when it shouldn't.

 

Two often overlooked sensors can make the heat do weird things,. One is the ambient air sensor. I couldn't get heat unless turned all the way to high. After checking the ambient air temp sensor said it was 136 degrees outside and the system would keep the AC running to cool me down, unfortunately it was December and I needed warming up not cooling off.
The other sensor is the cabin temp sensor if either one is reading cold outside or inside you are going to get heat.

 

See Item 5:


(click on the image to enlarge it)

From the difficulty of previous repairs on one of these, I think they started with the AC unit and built the vehicle around it!

Graham

 

Graham and all. Yeah I get black/grey foam pieces out of the AC some too. However using auto as the default mode is giving me good results, the unit cools/heats according to the temp set. Nice.
Tom and Miss Kitty