My air won't work, but all the controls function properly. Relay clicks when going from A/c normal to A/C max. Fan blows through the ducts, but the (light Blue wire ) at the low pressure switch, under the hood has no power at all. So the compessor clutch will not cycle for lack of power from the low pressure switch. Could I get an A/c electrical diagram from someone so I can back check the light blue wire to its source. Any suggestions from anyone is appreciated. I am in Ormond Beach Florida, so if the air don't work - the car don't go. Thanks

Wiring diagram shows a light GREEN, and a tan wire at the pressure switch. The only light blue wire on the diagram is for the blower motor resistor.

btw...if ya'll want to, whoever needs this diagram, click and save it to your 'puter, and I'll remove it after a few days, because it IS too large.
Also, for youse guys with 77s, I can send you a PDF file for the A/C that includes this diagram, and vacuum diagram, as well as repair info.

Make sure you have a full charge. If you don't the system will not cycle and will shut down. By the looks of the diagram the tan going to the cycle switch is hot. If the system is fully charged and the switch is ok then the green going  to the compressor should also be hot and turn the compressor on. 

Adam, You were right about the low pressure switch wiring. But my C3, I found out, was born in August of 77 & therefore has a R4 compressor, so I think I need a 78 diagram. Because the wire colors, basically the TAN wire, to the low pressure switch & the idle stop solinoid, is in fact a light green. The other wire leaving the low pressure switch is light blue & goes backto the compressor control switch. The sight bubble looks clear @ the low pressure switch, so you think I should add a pound of R134 to see if it starts to cycle or not. I would like to see the 78 diagram though before I get involved. Thanks again.

The sight glass will only be useful with the system operating....it has to have refrigerant flowing thru it to be able to see it in the glass.
I'm pulling the '78 system info now....it's taking a while, since I have to use IE instead of Firefox for this particular program.....arrrgh!

Finally got the info d-loaded, and e-mailed....whew! The '78 diagram for the AC is different, and shows the correct wires colors....