1956 A/C Compressor won't switch on

[Charlie CLC#18187]

Is there a low pressure cut-off switch on a '56 a/c system?  I am trying to get the a/c running- it's all there and looks to be in good condition.  I am sure the charge is gone and probably compressor seals leak.  The compressor will run if I jump it directly from battery.  If I switch it on with the regular controls, the idle kicks up, but the compressor won't engage.  Power is not going to the compressor through the black wire. 
I won't run the compressor with no charge in it, just want to make sure the circuits are working properly.
Thanks for the help.

Charlie
           

[Jon S]

Even with power in black wire, compressor will not kick on unless there is a minimal charge in the system.

[J. Gomez]

Charlie,

Check the following post; I’ve uploaded a wiring diagram for the A/C that would help you isolate your problem.

http://forums.cadillaclasalleclub.org/index.php?topic=98421.msg266432#msg266432

There is no low pressure switch in the ’56. If you follow the positive path for the compressor solenoid the +12V is from the 3-way switch and the temperature control lever at the control panel.

If you move the temperature control to max/full the lever wiper (Dark Green) would make contact with the Dark Blue contact extending the +12V up to the evaporator (rear unit) freeze thermostat.

The thermostat contacts should be closed under normal condition, this will extend the +12V back to the control panel via the Black. There is a connector at the control panel hardness which the Black wire is connected to the compressor.

I would start with the control panel; check the temperature control lever, moved the lever to the max/full position and verify the contacts they may be broken or corroded.

Good luck..! 

[Charlie CLC#18187]

Thanks Jose.  I'll follow your recommendations.  I also checked the thread you started on A5 rebuilding and saw what I could be dealing with.  It is extremely unlikely that mine doesn't need new seals at a minimum, I suppose. 

Charlie