Im here in afghanistan, big fridge isnt working. evac down no leaks, fill up with the prescibed 13 oz 134. No cooling activity whatsoever. Compressor is on. Only 90 psi low side w/ 13 oz. Add more- can only get 120( the bottle pressure). Has a presribed 140 psi working pressure. Seems like the compressor is moving but doing little pumping. What u say?

You can have a leak if is small put can stop leak if this not works you have a large leak.

When the compressor is replaced it should have had at least 2oz of oil inserted into it. The entire system should have been flushed to remove any foreign debris ( especially if the original compressor/clutch failed ). The system then needs to be vacuumed down to remove any moisture for a minimum of ten minutes and then leak tested to ensure vacuum holds. The system is then filled with the proper charge of freon and oil and then monitored for guage pressures and signs of leaks to ensure proper operation and effective cooling

either low gas or a the compressor soloniod /clutch packed up their the two most common causes

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If there is no cooling at all , before we go further we must confirm the first step of confirming the compressor and gas pressure. So shut off the fridge and leave it off while you clean and check the evaporator for frost. If frost is seen it is a good indication as the compressor is working with sufficient gas within.
Now after about 6 hours plug in the fridge to start. Observe cooling to happen in about one hour and ice to from under three hours.
Earlier make sure that the thermostat was set to normal mode for freezer and fridge. If there is no ice formation we have a big issue as the compressor and gas must be checked out. If compressor is running check the pressure, get help to test gas pressure. If not you will need to fill up ,If gas pressure is good the possibility of the compressor being inefficient is high. In such a case you must take consensus to estimate and decide, if RPM of motor is low check capacitor.
However if Ice forms then observe the fridge for about 24 hours for cooling to continue and the fridge to cut off . If not the auto defrost timer, or the thermostat must be checked.
If defrost timer works but frost keeps forming check while the compressor shuts if the heaters are working, check continuity of the heaters.
So try this test from the outside and make your observations so that we come to the solution. If not take an estimate and decide before a serious work is taken up.

Both sides are to low. High side should be closer to 350psi and low side should be around 65psi. Im thinking you didnt but enough 134a in (should of used around 5.3 cans) or you have a leak that bleeds off at a certain pressure. Get a can of stop leak with leak detector die put that in turn A/C on max drive it for a day or to then in the evning when its starting to get dark take a bright white LED flashlight and inspect all A/C parts if you have a leak the die will luminate allmost glow. Try that and let me no what the results are.

if unit is very old the compressor may be the noise but look at fans and tubing as a cause of the noise first . and the rubber insulator under the compressor . if you have a gas leak the unit will not cool and you cannot smell it . most units only use .5 oz of gas . this will not be dangerous . ps not good so smell it but generaly its harmless .. mm R 12 AND 134. ARE VERY SAFE ..

TAKE VECHICLE TO A GARAGE THAT DO AIR CONDITIONER WORK BECAUSE 1988 MODEL MORE LIKE HAS R-12 FREON. THAT WONT MIX WITH R - 134 REFRIGERANT THAT WOULD DAMAGE YOUR AC SYSTEM.

If the freezer is working like it should, then the cooling system is also working like it should as well. Nothing wrong with control panel or thermistor.

If the fridge compartment doesn't cool down, you may have too much in it hindering air circulation, or perhaps the door gasket is leaking.

Most side by side units have 2 compressor units. If you listen for it, you should be able to hear 2 compressors with slightly different pitches, operating at different times, or sometimes at the same time. If you never hear the fridge side compressor turn on, a sensor or the compressor is probably bad, if you never hear the fridge side turn off, the temp sensor is bad. If it has ever, or is leaking in the back, then there is a puncture in the cooling system, and the fridge will not be able to be cooled. If you can pull the fridge out and examine the tubes or unplug it for about 10 minutes and plug it back in to observe compressor activity and any small leaks, it would give a more definite answer to the problem. A mechanic will most likely be necessary.

The most likely cause is a gas leak . Call a technician.