AC will blow cold air at max setting but will not at low or medium setting

Hello, That sounds like a bad blower motor resistor if it does not blow at all on the lower settings, but it will on high. Now, if the air conditioner is blowing warm air at low speeds and cold air at high speed, it may be time to get back to the Jag specialist. Reason being is I'm not aware of any component on the XJ6 that would allow that to occur. I don't think they have staging like the BMW's did in the 90's.