The gauge reading should be between 2psi-6psi assuming its on the low side port which it likely is.. if the line is not getting warm then it is likely not compressing, could be a bad valve within the compressor.. it will run without freon ..
I am not familiar with this particular model but did a quick check and see there are several reported issues with the compressor and model design.
You can shut off the refrigerator and with the gauge hooked up the reading should climb to somewhere over 30psi .. if not then it sounds as though it has lost freon as well.. could be a small leak from when the compressor was last replaced.
A more seasoned tech should be able to replace the compressor with an alternate universal compressor, however I am not sure how that works with the newer PC boards.. I retired 15 yrs ago about then time appliances started being controlled more by software than actual components so this may not work on some newer appliances, foreign or domestic.