Hussmann racks in a Costco. The compressors have discharge check valves mounted about 3 feet from the discharge of the compressor. I have 2 racks, and each has a compressor that makes a god-awful noise after it cycles off.

I assume it is the reverse rotation induced by the captured discharge gas in the 3-foot piping. Why it only happens to one compressor on a ten-compressor rack is puzzling.

I asked engineering if there is anything to concern me and was told not to be concerned.

These compressors are equipped with Trax-oil controls which use 3 small magnets on a tiny float to induce a field that energizes or de-energizes the oil feed. These magnets were fouled with iron shavings on the compressors that made the noise. Further, at least one of them was covered with iron fur on the magnet at the outlet. I don't know why there is a magnet on the outlet.

Visual inspection of the other Trax-oils showed no filings.

Do you think it is possible that the short reverse-burps are delivering shavings or filings backward through the Trax-oil controls? Is anybody familiar with Trax-oil controls?