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1972 Mark ATC Box Questions

Hello Bill!

I'm writing from middle Europe, please excuse me for my English.

My heating system works like it won't accept the signal from the temperature lever. Always heat.

I took out the ATC box and did the test step by step which is in the factory service manual. It passes every single step, except were I test the amplifier and transducer. (the transducer stand alone test is passed too). I attached the page for better understanding. I examined the amplifier panel. All the resistors are ok, the adjustable resistor ok too. So in my opinion is that one of the transistors is misbehaving or destroyed. But because there is no identification number on them, it seems a dead end for me. Can you help me out on this? What kind of transistors are they, and is there any replacement transistor for them?

Best Regards,



Hi Attila -

If your ATC box is in good order you will need to perform the other tests shown in the manual on other components in the system. For instance if the "sensor string" has an open circuit or the system has a loss of vacuum, the ATC defaults to full heat on most models.

If the ATC box is in fact faulty we can test and overhaul this item for you as this service is a common repair item for us. We do have replacement amplifiers for the boxes in the 66-77 Lincolns and Marks. But again, we can offer you the rebuild service if needed.