Installation and Commissioning
Installation and Commissioning
This domain tests practices that determine reliability: line sizing, brazing, leak testing, evacuation, charging, and airflow verification. The exam expects order-of-operations reasoning, not just component recognition.
Core rules
- Use the manufacturer's line sizes and equivalent-length allowances. Too-small suction lines add pressure drop; too-large lines can cause oil return problems.
- Purge nitrogen through the tubing while brazing to prevent internal oxidation. Use a nitrogen regulator and a low flow.
- Pressure-test with dry nitrogen, never oxygen or refrigerant, and follow the manufacturer's test pressure. Leak-test joints before evacuation.
- Evacuate with a vacuum pump and a micron gauge at the system, isolated from the pump. A standing vacuum decay test detects leaks or moisture. Many manufacturers require 500 microns or lower; follow the specific instruction.
- Charge by weight when possible. If charging by superheat or subcooling, use the correct saturation temperature (dew point for blends) and documented target.
- Commission airflow: verify blower speed, static pressure, filter condition, and temperature rise or drop against the data plate.
Worked example
A split system holds 500 microns when the pump is valved off, but rises to 1,800 microns in 10 minutes. Reasoning: a fast rise indicates a leak or moisture; a slow rise can indicate moisture or a small leak. Do not release refrigerant. Pressurize with dry nitrogen and leak-check, then re-evacuate. If the rise persists, use a nitrogen sweep and a new filter drier, and repeat the decay test.
Traps
Using manifold gauges as a vacuum gauge; evacuating with the micron gauge at the pump; charging vapor into a zeotropic blend; and ignoring line-set length or airflow. Also, adding refrigerant to correct low airflow can mask the real fault.