Inside a Semi-Hermetic Compressor — Motor and Pump in One Housing
Open the side of a semi-hermetic compressor and you see two machines in one — an electric motor and a gas pump, sharing a case and the refrigerant that cools them both.
Most refrigeration compressors you meet on cold rooms and racks are semi-hermetic: the electric motor and the piston pump live in one bolted housing. You can see both here — the copper motor windings on the left, the cylinders and pistons on the right, with the head off.
This is why a "burnout" — shorted, blackened motor windings — is so often really a refrigerant or load problem in disguise. The motor did not just fail; it cooked because the gas that should have cooled it was not there. Fix the burnout without fixing the cause and the new motor follows the old one. The clues are in the running current and discharge temperature over time. I keep that per-unit trend in R-Pro, so a burnout is read as a story, not a surprise.