Air Conditioning Repair Installation and Evacuation Procedures Questions and Answers

Question 1

What is the primary purpose of flowing a small amount of dry nitrogen through the copper tubing while brazing a line set during an AC installation?

Accepted Answer

To prevent the formation of copper oxide scale inside the tubing

Answer

When copper is heated to brazing temperatures in the presence of oxygen, a black scale (cupric oxide) forms on the interior surface of the pipe. This scale can flake off and travel through the system, potentially clogging the metering device or causing damage to the compressor. Flowing a low-pressure stream of inert dry nitrogen displaces the oxygen, preventing this oxidation from occurring.

Question 2

A technician is performing an evacuation on a newly installed system. After isolating the vacuum pump, the technician observes the vacuum level rises from 400 microns and stabilizes at 1,500 microns. What is the most likely cause of this behavior?

Accepted Answer

Moisture is still present and boiling off within the system

Answer

When a deep vacuum is pulled, the boiling point of water drops significantly. A vacuum level that rises and then holds steady indicates that trapped liquid water is boiling into vapor, which increases the system pressure. Once all the liquid has boiled off, the pressure stabilizes. A leak would typically cause the pressure to continue rising towards atmospheric pressure.

Question 3

To ensure the most accurate reading of the system's vacuum level, where should the micron gauge be placed?

Accepted Answer

As far away from the vacuum pump as possible within the system

Answer

Placing the micron gauge as far from the vacuum pump as possible (e.g., on a port on the far side of the system from where the pump is connected) provides the most accurate reading of the entire system's dehydration status. Placing it at the pump or manifold can give a deceptively low reading, as it measures the vacuum closest to the pump itself, not the conditions within the entire system.

Question 4

During a new split-system installation, which of the following practices is critical for ensuring proper oil return to the compressor and preventing liquid slugging, especially with long line sets?

Accepted Answer

Ensuring the suction line is fully insulated and properly supported

Answer

The suction line carries cool refrigerant gas and entrained oil back to the compressor. It must be fully insulated to prevent the gas from absorbing excess heat, which would reduce system efficiency and capacity. Proper insulation also prevents condensation from forming on the outside of the pipe. Proper support prevents sags where oil could become trapped.

Question 5

When pressure testing a new R-410A system for leaks, what is the appropriate substance and procedure?

Accepted Answer

Pressurize with dry nitrogen to a pressure recommended by the manufacturer, typically around 250-450 PSIG.

Answer

Dry nitrogen is the only approved gas for pressure testing refrigeration systems because it is inert and moisture-free. Oxygen must NEVER be used, as it can react explosively with refrigerant oil. Compressed air contains moisture, which is a major system contaminant. The test pressure should be based on the manufacturer's recommendation for a static leak test, which is often higher than the normal operating pressure to ensure system integrity.

Air Conditioning Repair Practice Test

Air Conditioning Repair Practice Test

Air Conditioning Repair Installation and Evacuation Procedures Questions and Answers