Low pumper compressors can be devilish to diagnose properly. None of us wants to replace a compressor that is not bad. With more than 40 years of experience, I want to offer some thoughts.
First, calculate the actual compression ratio (CR). Convert high- and low-side gauge pressures to absolute by adding atmospheric pressure to each reading. I find 15 psi to be close enough for my purposes (e.g., 5-psi suction + 15 psi = 20-psi absolute; 85-psi discharge + 15 psi = 100-psi absolute.) Divide discharge absolute by suction absolute to obtain compression ratio to 1.