“The compressor did not burn out. It did not smell bad when I opened the system,” the service tech said as he ordered a replacement compressor from the distributor. While it's true that a bad burnout generally has an acidic odor, it's not always the case. To determine if the burnout is severe, the acid content and color of the oil will give a more accurate picture.
A system burnout must be cleaned properly. Most of the contaminated oils removed with the bad compressor when it is replaced. Some of it, however, remains in the system. A heavily contaminated system may require that the refrigeration lines be cut and the system be purged with nitrogen. This would assist in removing a majority of the contaminants.
The filter-drier cleaning method is the method of choice for a compressor burnout. In this method a properly sized burnout-cleanup type suction line drier is added to the system. This temporary drier remains in the system and removes acids and contaminants during the cleanup process.
A few precautions should be observed. Critical charge systems require an additional refrigerant charge if an oversize liquid line drier is used. There is no additional refrigerant charge needed when using suction line driers. Pressure drop across the suction line drier, however, should be monitored. After two hours of operation, check the system.
A severe system burnout can contain enough soot and contaminants to restrict the refrigeration flow quickly. You should return to check the pressures and oil for acid within 48 hours of operation. There are products and tests kits available to assist in the sampling of oil and testing for acid. If the oils still discolored and has a bad odor or tests to be acidic, the compressor oil should be changed.
Changing the oil may require removal of the hermetic compressor. After removal, carefully invert the compressor to drain the oil. There are also pump type removal tools available. Be sure to measure the oil removed from the compressor and refill with the same amount and type of clean fresh oil.
Allow the system to operate for an additional 48 to 96 hours and recheck. If the oil checks out OK, replace the liquid line filter-drier with one of the normally recommended sizes. Remove the suction line drier from the system. Charge the system and check the operation.
A note of caution: Always wear safety glasses and rubber gloves when performing burn-out cleanup and handle the contaminated materials properly.
Source: Hoshizaki America Inc.
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