NCT HVAC System Components & Diagnostics 3

Question 1

What does a technician use a psychrometric chart to determine when troubleshooting an air handling unit?

Accepted Answer

Air properties including dry-bulb, wet-bulb, humidity ratio, and enthalpy

Answer

A psychrometric chart graphically represents air properties such as temperature, moisture content, enthalpy, and relative humidity, essential for AHU troubleshooting.

Question 2

A scroll compressor is producing a loud rattling noise at startup. What is the most likely cause?

Accepted Answer

Liquid refrigerant slugging the compressor at startup

Answer

Liquid refrigerant or oil slugging is the most common cause of rattling or knocking in scroll compressors at startup, often due to refrigerant migration during the off cycle.

Question 3

In a split system with R-410A, the technician measures 420 psig on the high side at 95°F outdoor ambient. What does this indicate?

Accepted Answer

Non-condensable gases present in the system

Answer

R-410A saturated condensing pressure at 95°F ambient is approximately 380-400 psig; elevated pressure above this range suggests non-condensable gases such as air or nitrogen.

Question 4

Which type of metering device maintains a constant evaporator pressure regardless of load changes?

Accepted Answer

Automatic expansion valve (AXV)

Answer

The automatic expansion valve (AXV) is designed to maintain constant evaporator pressure by modulating refrigerant flow in response to pressure changes.

Question 5

A cooling tower is experiencing white mineral deposits on the fill media. What is the corrective maintenance action?

Accepted Answer

Increase blowdown rate and treat water to control scale formation

Answer

Mineral scale on cooling tower fill is controlled by increasing blowdown to lower cycles of concentration and using scale inhibitors in the water treatment program.

(NCT) NAFA Certified Technician Practice Test

(NCT) NAFA Certified Technician Practice Test

NCT HVAC System Components & Diagnostics 3