I've searched and wasn't able to find a thread that matches my issue exactly.

The AC started fluctuating between cool and warm. I was assuming low on refrigerant. I put my O'Reilly special can with gauge on the low pressure valve and the gauge read in the green (~35psi). At this point I noticed that my compressor clutch was not kicking in. Assuming a bad compressor/clutch I replaced the compressor with a new FoMoCo unit. Now all I get is hot air. I checked the voltage at the pigtail for the compressor and I have zero volts. I have checked the AC Clutch relay (#30) as well as the AC Clutch Feed fuse (#47) and both of those were good. I have checked the volts at the High Pressure switch and had readings of 4.9v, .02v and .02v. Mind you, this was tested with the power on and the AC blowing, but the truck was not running due to the proximity of my hand to the belt and pulleys. Does the truck have to running to get power to the switch? If not, why wouldn't I be getting power?

It got dark and couldn't immediately locate the Low Pressure switch. Anyone care to give me some insight as to where it might be located?

The switch is located on the passneger side down the side of the radiator. It is not real difficult to get to but it will be a bit tricky to get it off should you need to replace it. The easier way to test to see if you need to replace it would simply be to jump the relay. Basically just get an insulated bit of wire with both ends stripped then remove the relay and jump the two holes that pass power through this will bypass the switch. If the clutch engages then you probably have a bad pressure switch. I was going to say your clutch could be bad but since you already put a new compressor on that rules it out. My Ac did a similar thing though I'm inclined to believe the clutch simply got rusted and would not engage.

And so it continues. Swapped out the pressure switch for a brand new one and still no cold air. Guess it's gonna require a trip to the shop.

If you have not taken it in yet do this one thing first to possibly save yourself money. With the truck on and the ac put to max go under the truck (carefully obviously lol there are guards but yeah you'll be close to the fan) with a non magnetic piece of metal say a flat head screw driver and put it against the outer pulley of the ac compressor. If you feel magnetic pull but it's still not engaging then one of two things is the cause either your coil is going bad or the clutch is going bad. DO NOT let the shop give you some bs about needing this and that to fix it. That is what happened to me I went in wanting them to replace the clutch or the coil or both because I knew that was the problem (I just did not want to piss with it lol) they came back trying to say I needed a new compressor and the whole system basically. So I left and since I didn't want to piss with it yet again I just bought a brand new compressor all set for like $240 on rockauto and paid a shop like $200 to put it in. It's been working perfect ever since. After having to old compressor off it really appears as if the clutch became rusted and just would not engage anymore because the coil tested fine but even trying to force it down the clutch plate would not move well. So yeah if you have magnetic pull on your compressor coil with the ac on I'd bet money the reason is the same. You can try tapping the outer ring as well to get it to engage if you have magnetic pull and it won't engage I did that the year before and it started to work for a bit. Just remember the fan is right there so small taps ;-).