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1969 Mark AC Air Flow Control

Bill –
I was given your name and contact info by Chris Dunn at Lincon Land. I understand we all have something in common – all three of us have Mark IIIs without vinyl roofs! Certainly the way the designer had intended the car to be.
We need some advice with ours. We’re trying to get the HVAC to function properly and the problem at hand is the air flow control. We have a competent mechanic here in Palm Springs, California who is familiar with older cars but he has reached the limits of his experience with this particular issue. As you know – access under the dash is quite limited. We only have 35K miles on the car so we’re concerned about him randomly disassembling things.
We seem to be only getting air from the defroster. Chris tells me the ATC might be the culprit but we’re wondering if there is any advice you can give for troubleshooting to pinpoint if that is the case?
We are scrambling to get the car fixed before the Palos Verdes Concours and the LCOC National meet in San Diego. We will be driving and showing the car at both events.
Any help you can provide would be appreciated.
Scott –
The Automatic Climate Control system on your Mark III is a complicated system for its time and it is not easily and quickly understood and diagnosed. If the technician working on it is not skilled at automotive Climate Control systems in general and does not have the correct Manual and wiring diagram for that particular vehicle he or she will have a very difficult and time consuming job ahead. Some vehicles are fraught with several problems. Trouble shooting these mechanisms is always done with the proper Manuals etc. by your side. Your description of the one particular issue ” we seem to only be getting air from the defroster” could prove though to be an easy fix if you are lucky because if that system on your Mark somehow looses its vacuum supply to the ATC control box, the controls will automatically default to Full Defrost, High Speed Blower and Maximum Temperature output at any control lever setting. Therefore the first item to check should be the vacuum supply to the ATC control box with the use of the vacuum diagram. Loss of vacuum ( an unplugged/broken vacuum hose ) could be your only problem. Additional issues with other symptoms are possible however.
Good luck with a speedy repair.

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