I decided to take the transducer/amplifier board out of the programmer this time to see where the problem could be. It can be removed very easily - it's only held in place by 4 screws. Be careful not to turn the gear wheel with the potentiometer though as you would have to recalibrate it again afterwards.
After the board came out, I quickly found out where the problem was. Below is a picture of the removed board:
The transducer/amplifier unit was sitting pretty loosely on the circuit board, and one of the very thin and fragile wires going to the coil was broken, as you can see on the picture below:
When I turned the circuit board around I could see that the soldering points on the circuit going to the transducer and the amplifier were broken and that they no longer were making good contact. That was the reason why the system did no longer work.
The pretty simple solution was to re-solder the 3 soldering points and fix the broken wire going to the coil. I then put everything back together and now have a perfectly working ATC again. These old circuit boards can be very troublesome and I think that most of the time when a programmer goes bad on these 70s cars its probably a fixable problem like this. I was very worried that I would need an expensive rebuilt programmer and I am very glad that I could fix it by myself.
I have no idea though why everything worked when I put the car into storage last fall and how it broke while the car was inoperative…
Check my older post of the MKII programmer to also see the electrical diagram for the ATC system.
The programmer as seen through the glove box with the connectors and the plastic case removed
The 1977 / 1978 Eldorado MK II Automatic Temperature Control Programmer
The transducer which caused the problem (the golden part with the single vacuum line going into it)
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***
The vacuum checking relay and the electric connectors.
The vacuum power motor
from the 1977 FSM
Trouble shooting guide for when the system works in full AC mode only.
A color coordinated electrical schematic with annotations to describe the various functions of the system.