Factory A/C question, '72 GMC

[harrydunn]

Good morning--

I am wondering if anybody can tell me if my '72 with factory air has a low pressure switch that would keep the compressor from kicking on. The compressor kicks on fine but I don't want to run it too long if it is low on R-12.

Which brings me to my next question...

I found one A/C port on the '72 last night but could not find the second. I believe I found the low side port. If anybody could tell me where the second port is, I would appreciate it. The truck is stored at a friend's house and we didn't have good light to look under the hood so it may have been right under our noses.

Anything different about charging these systems compared to other vehicles? I've charged both R-12 and R134A systems in the past. Pretty straight-forward.

Thanks,

Mark