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Howard thank you for the response.  As I stated we did closely scrutinize all vacuum lines for any minutiae holes or cuts.  The manual shows a A/C system test device that was made way back to test the entire system.  Couldn't imagine anyone having this relic.  We'll continue to troubleshoot the system. Were looking for an electrical connection that triggers a vacuum actuator to close the doors.  The system appears to be electrical activated and vacuum operated.  For now we jerry rigged the doors to remain closed so I have maximum cooling air. They can be opened the instant defog is needed.  Your closing statement mentioned moisture on the windshield above the defrost/defog vents possibly from a a/c drain being plugged.  We turned the manual sideways and upside down and can't see the connection with the vacuum lines in the system.  Please explain this so we can ring it out.  Thanks again.

The evaporator will in all AC systems collect water out of the air like an ice cold glass in hot weather and that water drains down and if the drain tube is clogged it collects and too much moisture gets blown out the vents. This is true on all AC units for home or vehicle. But it is also noticeable when the AC is on and the blending doors are not blowing hot air but blowing cold air out an open defrost vent on the glass it too will collect water on the inside of the windshield and I had one that was so cold on the glass that it would collect moisture on the outside too and I had to turn on the wipers to clear it off.

The defrost vent should never be open with just the AC on. But keep in mind that the AC runs all the time even with full heat but if the heater core is stopped up or the door blending is wrong, the AC is on all the time and that will cause the windshield to frost over in the Heat / Defrost position.


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Howard M. Fitzcharles III


Jaguar from the XK 120 to XJ-6 ser. 3 1987


Dealership line mechanic on MG, Triumph, Jaguar for 15 years, Instructor in commercial mechanics school 2 yr. Product information manager for piston and valve manufacture, Instructor & hotline answer man for import car parts importer 15 yrs.

Associate member SAE EAA member

Import Car magazine

ASE Master Auto with L-1 certification up to 2000

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