A few general observations to start: Based on your pressure readings, it appears to me that all three cars are empty of refrigerant or nearly so. One of them, the 1990 Mercedes, originally used R-12 refrigerant unless it was converted sometime during its life to R-134a. Do you know whether that's th...

Very nice looking, clean Suburban by the way. I used to live in your area, so I know a little something about the Texas weather. Here's another thing you could try, although a bit of a nuisance: When you think it might be icing up, pull over and look at the drain tube underneath. If little to no con...

A few additional thoughts. Are you the original owner of this vehicle, and do you know whether the system has been serviced previously? Also, Al9 brought up an interesting point about the state of the charge. If you haven't already done so, I suggest having the refrigerant recovered and weighed to d...

I'm wondering, though, whether the evaporator is actually freezing up. When you think it is, do you also notice a marked reduction in airflow from the vents along with a change in sound from the blower?

Equal pressure on both the low and high sides also suggest to me that the compressor clutch might not be engaging and that you're seeing only static pressures. Are you sure the clutch is energizing, pulling in, and turning the compressor shaft when you turn on the system?

The correct adapters fitted to the red and blue hoses, connected to the system, will depress the Schrader valves when you rotate the thumb wheels fully clockwise.

Your pictures didn't appear, but I think I know what you mean. Why not make it simple? Return the can with the attached hose and purchase a can of R-134a (pure refrigerant only...no sealer or other additives), a valve for the self-sealing can, and connect the valve directly to the yellow hose from y...

Fan(s) working okay? I don't think you mentioned that previously. You did mention that the lines, hoses, and condenser appear to be open, although old hoses can deteriorate internally, not be obvious, and cause a blockage—something else to consider in a 32-year-old system. I don't think it's the com...

According to my references, the Crew Cab model takes 36 ounces of R-134a while the regular cab model takes 32 ounces. Charged directly from the small "12-ounce" cans without using the proper equipment, you won't notice that the actual amount each can holds often varies quite a bit. So I th...

Might be a combination of a clogged condenser and a bad accumulator, possibly with loose desiccant beads floating around inside. As someone else mentioned, if you're seeing +/–400 PSI on the high side, the compressor is doing its job. With those kinds of pressures, don't forget to wear your PPE when...