Jaguar Repair: Heat mode on AC, vacuum switches, heater control valve

Question
I hace a Jag 85, XJ6. Does the system require the outside temp of the car and the inside temp to be cold in order to get hot air out of the vents or defrost? I live in the south and with the humidity we have my windshield fogs up during rain. When I place the system on defrost and move the temp selector to hoter temp I only still get cold air. In no way or form can I get hot air out thru any vent. The heater water valvue is new and water goes thru the system.I gues with such a complex system several thing may be wrong or I may just need colder weather. Also, I have three sensors under my dash. From left to right what would the be the names of the temp sensors?
Thanks
Scott

Answer
Hi Scott,
You are correct about the system being complex. The heat is much easier to diagnose. When you have to defrost it doesn't matter what you set the temp to nor what the inside air temp is. It will blow hot air on the windshield. So just look at the arm on the heater control valve and start the engine while it is set on AC and automatic. Watching the heater control valve and have someone turn the control from Auto to defrost and see if the valve arm drops down. If it does the drum control of the vacuum valves is working. If it does not you need to remove the vacuum hose from the valve and put a vacuum gauge on it and switch the control to different positions to see if there is any control at all. Keep in mind that this system keeps the AC on at all times even in Max heat to cut down on humidity. All heat and air is controlled by vacuum controlled door blending other than the turning on or off of the heater valve.
If you have control out at the valve you need to get a manual from Jaguar on the car as the AC /heat system tests are long and complex beyond what I have out lined. An electric motor powered drum controls the system with many vacuum switches and electric switches.
Howard