Checking A/C freon pressure

[Pyrotechnic]

Pretty soon it's going to be time to start disassembly of my wrecked 78 once summer comes along. The deal is, I'm not sure if all the R12 escaped. The offending vehicle hit me pretty hard in the front, but the bumper and frame horns absorbed most of the shock, but the condenser up front is bent, but it does not look ruptured.

Is there a quick way I can check for presense of freon in the system ? I was thinking maybe a multimeter to one of the sensors/switches might tell me something.

If I do still have my R12, how can I get it recovered and keep it? There's a good chance I may swap the old Harrison log style compressor and some other parts to another truck as these parts, even the R12, were put in just a few years ago. I know R12 was expensive then, I'm sure it's not any better now if I can even still get it. I was surprised to be able to get it a few years ago.