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NATE LC Refrigeration study materials
NATE LC Refrigeration study resources

NATE LC Refrigeration: Refrigeration System Service and Repair

NATE LC Refrigeration · Work through your exam, one topic at a time.

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Refrigeration System Service and Repair

Domain 4: Service and Repair

This domain covers safe, compliant repair: refrigerant recovery, brazing, component replacement, leak repair, evacuation, and restart verification. The exam expects sequence and safety, not just the repair itself.

Core rules

  • Recover refrigerant into DOT-approved cylinders; never vent. Follow EPA Section 608 recovery requirements for the appliance type and refrigerant.
  • Before opening a circuit, isolate power, lock out/tag out, and recover refrigerant. Use a filter-drier on the recovery machine and avoid overfilling the recovery cylinder; observe the 80% fill limit.
  • Replace the filter-drier whenever the system is opened. Match flow direction and size the drier to the line.
  • Braze with nitrogen flowing to prevent cupric oxide. Heat-sink valves and controls. Pressure-test with dry nitrogen, then evacuate to 500 microns and hold.
  • When replacing a compressor, match voltage, phase, refrigerant, and oil. Check crankcase heater, start components, and rotation on three-phase.
  • After repair, charge by weight, verify superheat and subcooling, check amp draw against nameplate, and confirm defrost operation.

Worked example

A semi-hermetic compressor has failed. Recover the charge, disconnect electrical, cut the suction and discharge lines, and remove the compressor. Install the new compressor with new gaskets, replace the liquid-line filter-drier, and purge nitrogen while brazing. Pressure-test to the manufacturer’s test pressure, evacuate to 500 microns, and hold 15 minutes. Charge by nameplate weight, then check running amps against RLA and verify superheat. Reasoning: skipping the drier or nitrogen purge leaves acid and scale that cause repeat failure; weighing the charge prevents guessing.

Traps that cost marks

  • Venting refrigerant or using a recovery cylinder without checking fill level.
  • Not replacing the filter-drier after a burnout.
  • Brazing without nitrogen and contaminating the system.
  • Starting a compressor before evacuation or without crankcase heat.