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1969 Mark III ATC Questions

Hi Bill,

Last September, you gave me some great info to help get my AC working properly on my 1969 Mark. Unfortunately the cold weather crept up on me and I never got a chance to work on it, but when I get the chance to get started, I wanted to know this: Is there a way to manually override the temperature door (door to change from heater core to AC evaporator) so that it is always in the "COLD" position. I want to do this because I honestly believe that this part of the system in not working properly and I want to rule out the ACC control system. I'm not sure if this servo is electric or vacuum, or a combination of both but I'd like to override. I think the default position for this door would be full heat/defrost.




Hello Dan -

The Automatic Climate Control system on your Mark is a complex system therefore accurate diagnosis is necessary to properly repair them to the condition that they were in when they were new.

I have found over the years that 99% of the failures are within the Control Boxes and the Servo units. Other support systems and sensors etc. can also fail but most problems can be found in the above components.

We have perfected and do offer a service to overhaul these two parts so that they operate " as new". If the rest of the system is in good working order with respect to the refrigeration system, the heating components and sensors etc. the ac/heating system will operate as it did when it left the factory after the ATC box and SERVO are overhauled.

All of the tests and operations are shown in the factory shop manuals. I recommend that you purchase one if you do not have one in order to accurately understand the system operation and diagnose your problems. If you believe that bypassing the automatic controls will aid you in some meaningful diagnosis, you will learn this also from the manual.