I have a slight problem......No AC!!!!

Does the fan run on all speeds?
Does the heater work when turned to heat?
Vacuum doesn't control the compressor kicking in...that's all electrical.
Check the ground wire(black) coming off of the compressor plug, and make sure it is connected tightly to ground. Check for 12v at the green wire on the plug(key on, A/C & fan on max). No voltage means either the high pressure switch(in the small A/C metal line) is bad, or the low pressure switch(usually mounted on the accumulator/dryer) is bad, there is no refrigerant in the system, the fan switch is bad, or the compressor "on" switch in the control panel is bad. By "bad", I also mean it could just be a loose connection.
Try jumping across the terminals of the pressure switches to see if the compressor will kick in. If it kicks in when you jump the low pressure switch, check the refrigerant pressure before going any further.

btw...the '77 could have either type of A/C system: The older style VIR set-up with the A6 compressor, or the newer style, with the orifice, accumulator/dryer system with the smaller, R4 compressor. Which does yours have? Adams' Apple2007-06-20 10:04:46

1. fan run .. yup, all speeds, on normal ac speed adjust. on max , fan runs at high speed and adjusts to vents

As usual, Joel is right on the money.

I just checked the system. no Pssssst, when you press the valve core on the shrader valve. Not even a little bit. I only found one in-line cut off. it is mounted to the Pass side fender well. the in-line pressure switch let the compressor fire up when I jumped it. I have no clue what one i have.

Something had to have ruptured if you have no refrigerant. Star at the front of the car with the condenser and work your way to the cabin. Maybe you can rig a compressed air test source to see if you can hear the leak.

Scott

If there is no obvious signs of leakage under the hood, it's possible the evaporator has a hole in it...not good...or easy to fix.
Have you converted your system to use 134, or is it still R12? If your using 134, I'd say pump a can in it and see where it comes out. Also, you can buy dyes to put in the system to find leaks really easily. Try putting a can of freon in it first, to see if you can hear where the leak is. If you can't hear it, or it's not obvious where the leak is, use the dye. The dye requires a special ultra-violet light to see, but I have found that you can usually see the dye without the light, sometimes. The light I have works really well, but different dyes may require a different type of light. Your local auto-parts place should have the dye/light kits fairly reasonable.

This weekend I'll be Giving it my best shot. 134A. I'll try the dye first. I think I can borrow a light from work. The Motor T shop Is willing to help out.