1- With an x 1 scale multimeter, check for continuity and that the ohmic resistance is nonzero between the common and main, common and auxiliary coil terminals, and between the main and auxiliary coils.
2- With the multimeter at the highest scale of the device (minimum x 10K), make the mass test (current passing from the coil to the compressor housing), checking the continuity between the three terminals (common, main and auxiliary) and the compressor housing at a point where there is no ink. There can be no continuity, otherwise the compressor is defective.