Jaguar Repair: heater in 1987 XJ6, high humidity, vacuum valves

Question
The heater works in this car but seems kind of weak.  The windows steam up all of the time with quite a bit of moisture.  I live in an area with lots of rain and high humidity, but can something be done to increase the airflow of the heater fan?   Or is there perhaps something putting moisture into the heater air?  Please let me know your thoughts.  Thanks.

Answer
Hi Bill,
Yes, there can be moisture in the heating system. If it is coming from a leak in the heater core it will usually put moisture on the windshield and you can usually smell it. Other possibles are stopped up AC drain since the AC system runs when the heater is on. Also it is possible that the blend doors are not operating correctly and in the rain you are getting rain in from the fresh air intake into the car. As with any automatic AC/heat system they are complex and have several vacuum operated doors controlled by a rotating drum that opens and closes several vacuum valves depending on what is asked for. Another item is that there are two fans.
This system is difficult for a DIY to diagnose and repair and even difficult for an experienced mechanic with the manual to do.
My advice is first look for an experienced Jag AC/heater mechanic and if that is not possible, bite the bullet and purchase the factory series III service manual.
Howard