ATC acting funny between max cool and max heat

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ATC acting funny between max cool and max heat

Postby thegermanfan » Mon Sep 20, 2021 1:26 pm

My Mark IV automatic temperature control unit is making lots of clicking noise if in any position between max cool and max heat. AC is recharged and blows cold. Air distribution follows the logic of cooling out of the dash vents and heating the foot well. Blower speed control seems to function normally. But if I set in on an intermediate temperature, the box is clicking away like hell. Sometimes it finds a sweet spot and stays silent for a minute or so, then acting up again. Is this a common issue, or do I have to go through the full diagnosis procedure? The shop manual lists I think four vacuum gauges, a regulated vacuum source and some test lights as equipment needed for a full functional bench test. And the bench testing procedure seems quite involved. So I anyone has an idea, what could cause this erratic behavoir... I am open for suggestions.
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Re: ATC acting funny between max cool and max heat

Postby TonyC » Tue Sep 21, 2021 3:07 am

I know that chattery clicking sound cannot be normal; the only noise the ATC should make is the sound of the blower spinning. I'm only guessing, but it sounds like a relay in the master control could be acting up. I know from past experience that relays can make that kind of noise if their innards are getting corroded; when that happens the electric current is not passing through them like it should. Others with experience in ATC may be able to verify.

If my guess is right, that could involve some deep-down exploratory surgery. Thing is, even in the States finding somebody with experience in those older systems is extremely difficult...not impossible, the Usual Suspects would likely know how to do it, but I know that does not help an owner in Germany. Hopefully somebody here can give some guidance.

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Re: ATC acting funny between max cool and max heat

Postby LithiumCobalt » Tue Sep 21, 2021 10:42 am

The chattering was a common issue for the 60's ATC boxes, but I didn't realize that the 70's were also plagued with it. Doesn't mean that they weren't. For the 60's models, the chattering usually occurred when the desired temperature was satisfied and the "brain" was anticipating what to do next. In limbo, of sorts. You may get a hold of LincolnLand as many of these ATC brains are overdue for refreshing. Ford never intended them to last this long.
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Re: ATC acting funny between max cool and max heat

Postby thegermanfan » Tue Sep 21, 2021 11:27 am

Surprise! The issue resolved itself today! I exercised the temperature regulator and let the system switch between max cool and max heat several times. This seemed to make things better and after driving some time today, the system is as quiet as ever! So it must have been some light corrosion or dust on the switchplate that gets swept over by the servo arm inside the atc. The temperature lever itself could not have been the issue, because the erratic behaviour manifested itself when the system tried to reach a stable point. Which it does now with ease. *Heureka!*
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Re: ATC acting funny between max cool and max heat

Postby JimA » Tue Sep 21, 2021 11:41 am

I love it when problems cure themselves. "Course it might happen again but you now know how to put it into remission.
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