Low side or high side A/C charge port

I am at an old car show and the wireless internet is not working very well. The photo did not show up. Regardless, the low-side port is on the compressor or the line coming to it from the firewall.

Be aware that refrigerant can cause frostbite and blindness. Professionals wear gloves, safety glasses, and a face shield. The ports are different, so if you get the wrong one, the fitting on the hose will not fit.

You should not be low on charge with such a new vehicle. There is no way to know how much refrigerant is in the system now without recovering all of it, then adding a measured amount. Too much overcharge can allow liquid refrigerant to slosh into the compressor and lock it up or damage it. That also moves where it changes from a liquid to a vapor. Where that happens is where it becomes cold, and you want that to be in the evaporator in the dash, not in the hose under the hood going to the compressor.

That appears to be right. The top pipe that winds around the strut tower should be coming from the condenser in front of the radiator. That would be the high side. The lower fitting should be on the pipe going to the compressor.

Be sure to reinstall the black plastic caps on the ports when you are done. Those valves will leak. Their job is only to hold the refrigerant in while you're putting the caps on. The caps have the o-ring seals that stop any leaking.

90 psi on the high side is low and indicates low charge, but I am not good at judging performance based on gauge readings. The problem is the low and high side gauge readings will stay fairly constant from a half pound under-charge to a half pound over-charge. The system is filled partially with liquid and partially with vapor. Adding more refrigerant just changes the locations of where it changes between the two states.

Also, the pressure of refrigerant under pressure with the system at rest will be very close to the air temperature around it. If it is seventy degrees in your garage, you are likely to find close to 70 psi on both gauges. If you were to release one pound to the atmosphere, some of what remains in the system would turn to vapor and expand, and the pressure would go right back to where it was. No matter how much you bleed off, the remaining liquid will keep expanding and vaporizing, and the pressure will stay the same, until it is fully vaporized and there is no liquid left.

I prefer to use a thermometer to verify the system is has the correct charge, (after I have added the measured amount). The pressure is regulated to not go much below 40 psi in the evaporator because that equates to about forty degrees. Any colder and you risk getting below thirty degrees at which point the condensation would freeze into a solid block of ice that would block air flow. The goal of the AC system is to only lower the air temperature about twenty degrees. It is the removal of the humidity that creates the comfort. Lets face it; sixty degrees is not comfortable when you are sitting still for long periods.