1998 XK8, I replaced timing chains and tensioners about 6 months ago. I followed the instructions on this forum except that I removed the radiator so I could get a impact wrench on the harmonic balancer. EVerything went very smoothly and it runs like a top, but first cold weather hit and I have no heat. I don't know if I screwed something up during the timing chain repair or if this is all new. The air conditioning is going full blast when on AUTO. Even when I set the thermostat to 80 F, the A/C still runs full blast! I did a hard reset yesterday, but no change. The only other thing I have done is take it to a transmission shop and had the transmission fluid dipstick mod installed because I couldn't get the fill plug out myself. Any help would be greatly appreciated, it's getting chilly!

 

I had similar problems with my heat. Try the following steps.
1. Crank the temp with the red button up to HI. Do you get heat?
2. Push the EXT temp button. What does it read?

With mine i could get heat only on HI. When i pushed the EXT temp button it read 136 degrees. Climate control was seeing that it was really hot outside in December.

The problem may be the EXT temp sensor, it is mounted under the front bumper cover on the passenger side. When removing the radiator you may have disturbed it, unplugged it or damaged one of the wires.

I would start looking there before getting into the other areas of the cooling system.

 

Also, in the system check it says to press the FACE to advance through the fault codes. What is the FACE?

 

I had the same problem after changing my tensioners, chains & water pump. I ended up not using the car for 3 months because It was so cold, read hundreds of threads and somehow stumbled on 1 that said are your front fog lights working, I looked and they weren't changed a 5amp fuse for the switch and to my amazement it also controls the heater switch for hot air circulation, saved me a fortune, I new the system was working and did not want the cost of draining it again. Good luck

 

I had heater problems in my 2007 XK8 which were resolved by disconnecting the battery for 30 minutes then reconnecting, this allows the computer controlled system to reboot and reset all controls,

 

Quick note: it is correct for AC to run when on AUTO regardless of the temperature.

The AC dehumidifies the air, and then it runs through the heater. The engine puts out plenty of heat to fight the AC.