1968 DeVille conv Climate Control issues

[cadillacmike68]

OK, after having the heater core replaced the Climate control was completely inoperative. They Broke the plastic vacuum manifold. But after I replaced that I still got no fan. I had some ATC experts look at it and they replaced the dash control with my spare - the ratty one because I CANNOT FIND my two nice rebuilt and tested ones. Now there is fan the the arm on the power servo doesn't pull in when the temp dial is set to a higher temp.  Pulling vacuum on it beings the arm in and it holds, so the big doughnut on the power servo is good.

Is this the transducer or the amplifier on the dash control.

Does anyone have or know where I can get another dash control unit or get mine rebuilt??

["Cadillac Kid" Greg Surfas 15364]

Mike
When the heater core was replaced I'm sure a whole lot of vacuum lines were disconnected. I would start with verifying they are all connected in the correct places and not leaking
Greg Surfas

[cadillactim]

Mike

If the automatic control worked before the heater core was replaced, then it is unlikely that your transducer or the dash control is the problem. If everything worked before then I would check the vacuum lines from the engine to vacuum reserve tank, then from tank to transducer, then transducer to power servo.

No battery voltage to transducer will drive system to full heat. Since it is not defaulting to heat I would be looking for vacuum issue in transducer vacuum circuit or leaking power servo. Unplug the wire from the transducer and system should go to full heat.

Tim

[Scot Minesinger]

What Tim wrote.

Honestly, these repair shops...  They are all terrible.  I just fixed a climate control on a 1970's Cadillac that enjoyed a 100k (yep) restoration, and the restoration shop could not get the climate control working (especially the ac).  If you omit the heater control valve, pipe the heater control vacuum line to full vacuum, insert a small vacuum line into a larger one without a fitting (major leak), and fail to diagnose a bad fan relay (DOA), how can it even have a chance of working.  It was a super nice job and the owner was really nice, but the climate control work...

[cadillacmike68]

What gets me is that the transducer part Was working. I could see the arm pull in when I changed the dial from 65 deg to 85 deg. Now it doesn't teem to be.

I'm going to have a close look at Tim's book to see if there is a test for the transducer.  I'll also do the wire test and get the vacuum diagram out again.

[Scot Minesinger]

The transducer test is easy.  Remove it (one screw, which is also the ground), unplug vacuum and electrical.  Then connect a wire to the mounting hole and ground it under hood.  Hook up a vacuum with engine running to input (the smaller line) and put a vacuum gauge on the output.  Power the transducer with 12 v and with engine running and look at the gauge.  Then remove 12V power and see what the gauge does.  It should go opposite to what it was, if with 12v it was 15psig-full vacuum (or zero), with power off it should go to opposite - zero (or 15psig).

The ground on these is terrible, the mounting screw relies upon compressed insulation to force a good ground connection, which after 50 plus years is no longer that great.  I usually drill a second hole thru the mounting bracket and connect it to a good ground with ring connectors on each end of the wire and thru bolts. 

["Cadillac Kid" Greg Surfas 15364]

First question Mike, going to the simplest first, do you have vacuum TO the transducer?
Greg Surfas