The air condition of my Cadillacs always surprise in a negative way. Every spring something new does not work after I wake them up from their winter hibernation.
This time the 67 Eldorado had a new problem which I had to fix.

It suddenly only blew hot air out of the AC outlets. It did not change modes at all. That was a sign of a weak vacuum signal…

I started to inspect all the AC related vacuum lines of the car which checked out fine. Next I did the test I´m describing here in an older posting, as I suspected that the power servo had a problem.
I soon found out that still not enough vacuum was supplied through the transducer.

That meant that either the transducer could be faulty, the temperature sensor could be defective, or the dash control head would not work properly. I took out the temperature sensor of my 67 Deville to test it in the Eldorado but it did not change anything.

I then removed the control head and tested it with a spare one I once bought cheaply on ebay. It did miss some connectors and switches, it had some blemishes on the chrome and did not look good enough to install it into any of my cars. When I put it into the Eldorado anyway the AC suddenly worked perfectly again.
So I removed all the electrical parts from this working unit and transferred it to the perfectly looking but defective control head. After I had swapped all the usable parts I put the unit back into the car and I now have a perfectly working unit once again.
It looks like that there was a problem in the amplifier part which translates the signal coming from the rheostat into a current going to the transducer which regulates the vacuum going to the control head and the power servo.
Lets see what issue comes up next spring…

The Rheostat when set to the lowest temperature setting shows around 2,5 Ω You can check if it is working with an Ohmmeter.edge
At the highest temperature setting the resistance is getting lower.edge
The Amplifier part of the control head is on the underside. Something in here must have gone bad on my control head. I will try to find out what went bad and repair it to have a spare part.
The 67 Eldorado is back on the road for the 2015 season.