Improper Refrigerant Charging Procedures Lead to Compressor Failure

At T/CCI we know that Performance and Durability Count. And we know that they count because our customers rely on our compressors to keep their vehicles running and their operators comfortable, even in the toughest environments. When a customer experiences issues with their compressor, it is our commitment to fully investigate the situation and offer solutions that will keep everyone up and running.

The Situation

While working with a customer who is contracted to provide MRAP ambulances to operations in Afghanistan, compressor failures were being reported. The following information was collected:

  • Most failures were immediate or shortly after delivery
  • Compressors showed extensive shoe damage
  • Significant swash plate damage was also reported

The Analysis

T/CCI engineers worked closely with the customer to evaluate the conditions, the protocols, and the failure details in order to conduct a thorough evaluation of the situation. Testing included hot chamber testing with oil circulation studies, internal lab simulation, and onsite testing with the customer. The following conditions were present:

  • original refrigerant charge level was 7 lbs.
  • total compressor oil charge level was 6 oz. in the compressor and 5 oz. installed in the discharge line during assembly
  • there was a darkened “star” pattern on all 10 shoes and a smudge through the center of the compression surface in an arc pattern
  • Thermal migration during transport may be an issue

The Conclusion

After completing a thorough situation analysis, the T/CCI engineers determined that the root cause of the failures was lack of lubrication between the swashplate and the “shoes”. The customer’s procedures called for initially charging the compressor with 1.5-2 pounds of refrigerant into both sides of the compressor. They then shut off the discharge valve and left only the suction open when starting the vehicle and engaging the clutch. The compressor then ingested approximately 7 pounds of liquid 134a through the suction port and through the crankcase. In this process, the refrigerant flow exited the compressor through the discharge port and carried away all internal lubrication. Without this lubrication, the bottom of the shoes rub the swashplate surface which resulted in the “star pattern” on the bottom of the shoe. These worn shoes smear aluminum on the swashplate until the shoes become dislodged and jam the rotating assembly, locking the compressor up.