HVAC System Components & Diagnostics Flashcards

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

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

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

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

Answer: Liquid refrigerant slugging the compressor at startup

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.

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?

Answer: Non-condensable gases present in the system

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.

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

Answer: Automatic expansion valve (AXV)

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

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

Answer: Increase blowdown rate and treat water to control scale formation

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.

A technician is sizing ductwork using the equal friction method. What is the primary design parameter maintained constant throughout the duct system?

Answer: Friction loss per 100 feet of duct

The equal friction method sizes all duct sections to produce the same friction loss per 100 feet of equivalent length, simplifying design and balancing.

What parameter does a manifold gauge set's compound (low-side) gauge measure that a standard pressure gauge cannot?

Answer: Both pressure and vacuum (inches of mercury)

A compound gauge reads both positive pressure and vacuum below atmospheric pressure (in inches of mercury), essential for system evacuation verification.