So I have an interesting case. I got this 1994 Corvette with the AC not working, found out it was the programmer unit under the dash that had the CPU shorted out and needed to be replaced. Last night I got the new one in the mail put it in and fired it up. Everything worked like it should except it wasn't blowing cold, and I noticed the compressor wasn't spinning. The problem was the low pressure switch was open because it was out of refrigerant. After adding refrigerant at while jumping the low pressure switch, it started working blowing cold air and didn't need the jump for the low pressure switch. Come to find out 2 hours later I tried to turn on the AC again, and this time everything worked but the compressor wouldn't spin start. I tried jumping the low pressure switch again, this time it didn't work and the low pressure switch doesn't have even have 12 volts to it. I tried checking fuses, all fuses look good, I tried checking high pressure switch but I'm not too sure how to check since it's a three-pin and I know one of them gets steady 5 volt and it's kind of complicated. No diagnostic codes on the a/c either, asides from fuze, high pressure, and low pressure, where could I be losing my 12v? What should I check next? Maybe it's not sending 12v in the first place? Head unit on dash was rebuilt and programmer is brand new

 

It would appear from this schematic that the cycling switch doesn't have 12v but rather gets a ground signal from the programmer and sends it to the PCM. Start at the programmer and see if it has a ground path according to the schematic.