2005 Silverado AC Diagnosis

I just bought a 2005 Silverado with 160k miles and I am trying to diagnose the AC system. Most of the time the compressor never kicks on and so it blows warm air. Occasionally the compressor does kick on and the air gets cool but the compressor will only run for maybe 5 seconds or less. Sometime it will run a little longer the first time but still less than 30 seconds.

I hooked up gauges to the system and high and low side show equalize to just under 100 psi. I took this as a good sign that at least there isn’t a leak. When the compressor kicks on the lowest I have seen the low side is about 55 psi and the high side barely rises and maybe gets to 125 psi. I guess this could be because the compressor isn’t running long enough to generate much pressure. I have also heard that this could mean and obstruction in the low side of the system.

I have also tried to jumping the low side pressure switch but that didn’t change anything.

What would be the next step, should I evacuate the system and vacuum it down to clear any moisture and try to recharge.

How would you diagnose this further. or are there parts I should just replace like the receiver drier?

Finally I am just trying to understand this AC system. Could you explain how the high and low side work. What I mean is the high and low ports are on the same hard line. From what I understand there is an orfice tube in the middle but I don’t know that that does.