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Fixing the 1978 Cadillac Eldorado´s ATC programmer. The AC works again.

****UPDATE****


An update to the article below can be found here as I had to repair the programmer again in May 2015:


The air-condition in my 1978 Biarritz did not work correctly. For some reason the system always stayed in full AC mode and no matter to where I put the temperature dial on the control head I could not get the heat on, no matter what I tried.
The shop manual is very helpful in trouble shooting the system. Its covered in the 1977 factory shop manual (FSM) as there were no changes made to the system in 1978.
It took me a while to fully understand how the system works - so I had to read the FSM multiple times to get the grip what is going on in the system.

First I inspected all the vacuum lines in the car to make sure that there was no leak anywhere, as the heating mode requires a very high vacuum at the vacuum motor in the controller.
All lines were in very good condition. I also checked the control head connections in the dash which were good as well.
I then suspected the vacuum motor in the programmer as it did not move. I removed the programmer from the car. You can access it from underneath the dash on the passenger side or even better if you remove the glove box lining through the glove box.
From there you only have to unscrew 5 screws, unplug the wires and the vacuum lines to get it out.

When I had it out of the car I checked the vacuum motor. I just sucked air through the hose and it moved and held vacuum perfectly.
The transducer or the amplifier in the programmer were most likely the problem.
When I checked the transducer which regulates the vacuum supply to the vacuum motor, I noticed that it seemed to not be connected to the electrical board as it should. I pressed it in, so that it made good contact with the board again and put the programmer back into the car and connected everything again.

***UPDATE 2015 - its not connected with pins but soldered to the circuit board - 3 of this soldering points were broken - the “repair“ I made here only temporarily worked. You have to check the soldering points for a permanent fix***

I started the car and the AC came back to life again immediately. I could see how the vacuum motor went through all the modes as it should according to the position of the temperature dial on the control head.
The build quality of the programmer obviously is not very good and the transducer somehow came loose causing the ATC to not work as it should. ***Update 2015 - it did no come loose but the soldering points broke***
After I tested everything I put the parts back together and can now enjoy a full working ATC in my 78 Biarritz again ;-)


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The programmer as seen through the glove box with the connectors and the plastic case removed

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The 1977 / 1978 Eldorado MK II Automatic Temperature Control Programmer

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The transducer which caused the problem (the golden part with the single vacuum line going into it)

1978AC-Programmer-SM-IMG_4712
The transducer is connected to the electrical board through a couple of pins - it was not connected properly and somehow became loose over the years - that was why the system did not work.
***UPDATE 2015 - its not connected with pins but soldered to the circuit board - 3 of this soldering points were broken***

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The vacuum checking relay and the electric connectors.

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The vacuum power motor
1978AC-Programmer-Diagram-SM-IMG_0206
from the 1977 FSM

1978AC-Programmer-Diagram-SM-IMG_0205
Trouble shooting guide for when the system works in full AC mode only.

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A color coordinated electrical schematic with annotations to describe the various functions of the system.

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1967 Cadillac turn signal switch arrived

Today another 1967 Cadillac turn signal switch arrived for my 67 Deville which is in the shop at the moment with a broken switch. I found a nice NOS switch on ebay and finally it's the correct one. All the ones I bought in the past were the wrong ones as 3 different ones were available in the 1967 models! Non of them is still in production or reproduced and they are very hard to come by. Originally they were built by AC-Delco and Boyne and they are very different as I learned later... I already spent quite a sum for wrong NOS switches. Used ones are usually sold for $250.- to $300.- at the big Cadillac parts specialists... Here is a picture of the NOS one I found - it was manufactured by Boyne.

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UPDATE 2010: In the meantime (since 2009) the Boyne switches they are getting reproduced and show up on ebay all the time. Also OPGI shows them in their Cadillac catalog. Its harder to find one for a T&T column as they are not getting reproduced so far. I do not know where one could find a switch for T&T though. If you know of any resource for T&T switches please let me know, I would love to have a spare one for my Eldorado!

When I was looking for a switch for my 1967 Deville, I only investigated resources for cars without T&T columns and this is what I found out:

According to the 1971 parts manual there are two different ones for standard column cars and one for T & T

  • 1967 - 1968 (Exc. T & T) Part # 7800483 - Switch, w/wiring harness (Delco-Remy)
  • 1967 - 1968 (Exc. T & T) Part # 7805675 - Switch, w/wiring harness (Boyne Products)
  • 1967 - 1968 (T &T) Part # 7805676 - Switch, w/wiring harness (Hazard warning switch an integral part)

The two different standard column switches can be identified without removal as the parts manual describes:
„Hazard warning switch is an integral part. Switches can be identified before disassembly as follows: The Delco Remy switch has a square hole for the hazard warning switch in the cover, the Boyne Products switch has a round hole for the hazard warning switch in the cover.“

The problem with the switch on my standard column DeVille was that the return cancel cam broke, and that non of the repair kits were available for the Boyne switch.

Replacing this switch in the steering column is quite a pain - below you can find the instructions from the shop manual on how to do it.
There is also a revised procedure for a much easier installation below in the “Cadillac Serviceman" from August 1967!

1967 Cadillac Steering Column

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Click on each picture for a larger view!

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The connections going to the directional signal switch - the turn signal switch connector

The Cadillac Serviceman from August 1967 shows a revised procedure for a much easier installation of the switch.

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If you need the shop manual instructions for a tilt and telescope column click here! Or just use the procedure above!


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