Refrigeration System Installation and Commissioning
Domain 2: Installation and Commissioning
This domain tests whether you can install light commercial refrigeration so it passes commissioning the first time: line sizing, piping practice, evacuation, charging, airflow, electrical supply, condensate removal, and defrost setup.
Core rules
- Follow the manufacturer’s manual for line size, equivalent length, oil traps, and maximum rise. Slope horizontal suction lines toward the compressor and install traps at the evaporator outlet and at the base of a riser.
- Purge nitrogen through the tubing while brazing to prevent internal oxidation. Pressure-test with dry nitrogen, never with refrigerant or oxygen.
- Evacuate to 500 microns or lower and hold with the pump isolated. A rising micron gauge indicates moisture or a leak.
- Charge by weight when the nameplate gives a charge, or by subcooling for a TXV system and superheat for a fixed orifice. Verify airflow before final charge.
- Confirm supply voltage, phase, disconnect, and overcurrent protection match the nameplate before energizing.
- Install a condensate trap on the drain; a missing trap lets air be pulled into the cabinet and causes water carryover. Check defrost termination and fan delay.
Worked example
A walk-in cooler TXV system has a condensing saturation temperature of 110°F and a liquid-line temperature of 100°F. Subcooling is 110 − 100 = 10°F. The sight glass is clear. After 30 minutes, subcooling falls to 4°F and bubbles appear. The reasoning: a TXV system should hold roughly 8–12°F subcooling at design conditions; falling subcooling with bubbles points to low charge or a liquid-line restriction. Do not add refrigerant until you leak-check and confirm the restriction location.
Traps that cost marks
- Charging a TXV system by suction pressure only.
- Skipping nitrogen purge and leaving carbon scale inside the tubing.
- Starting a three-phase compressor without confirming rotation and voltage balance.
- Ignoring drain trap and defrost settings during commissioning.