HVAC TROUBLESHOOTING & SYSTEM DIAGNOSTICS EXAM 2026 | VERIFIED QUESTIONS & DETAILED RATIONALES STUDY GUIDE

HVAC TROUBLESHOOTING & SYSTEM
DIAGNOSTICS EXAM 2026 | VERIFIED
QUESTIONS & DETAILED RATIONALES STUDY
GUIDE
HVAC TROUBLESHOOTING & SYSTEM DIAGNOSTICS EXAM 2026

VERIFIED QUESTIONS & DETAILED RATIONALE STUDY GUIDE


Question 1 What is the primary purpose of a metering device in a refrigeration system?

A. To compress the refrigerant

B. To remove heat from the condenser

C. To reduce refrigerant pressure and control flow into the evaporator

D. To filter moisture from the refrigerant

E. To measure the refrigerant charge level

CORRECT ANSWER: C RATIONALE: The metering device (TXV, fixed orifice, or
capillary tube) restricts refrigerant flow, causing a pressure drop that allows the
refrigerant to expand and absorb heat in the evaporator. Without proper metering, the
system cannot maintain the correct evaporator pressure and temperature.



Question 2 A technician measures suction pressure lower than normal and discharge
pressure lower than normal. What is the most likely cause?

A. Overcharge of refrigerant

B. Restricted condenser airflow

C. Low refrigerant charge (undercharge)

D. Faulty reversing valve

E. Defective compressor reed valves

CORRECT ANSWER: C RATIONALE: Low suction and low discharge pressures
together are classic indicators of an undercharged system. Insufficient refrigerant mass
in the system results in reduced pressure throughout. A restricted condenser raises
discharge pressure, overcharge raises both pressures, and defective reed valves affect
compression ratio differently.

,Question 3 Which refrigerant is classified as an HFO and is considered ultra-low GWP?

A. R-410A

B. R-22

C. R-134a
D. R-404A

E. R-1234yf

CORRECT ANSWER: E RATIONALE: R-1234yf is a hydrofluoroolefin (HFO)
refrigerant with a GWP of less than 1, making it an ultra-low global warming potential
refrigerant. It is increasingly used in automotive air conditioning as a replacement for R-
134a (GWP of 1,430).



Question 4 What condition does a high superheat reading at the evaporator outlet
indicate?

A. Insufficient refrigerant flow through the evaporator

B. Flooded evaporator

C. Overcharged system

D. Restricted condenser coil

E. Excessive compressor capacity

CORRECT ANSWER: A RATIONALE: High superheat means the refrigerant has fully
evaporated early in the coil and has been heated well beyond saturation temperature.
This indicates the evaporator is starved of refrigerant, caused by undercharge,
restricted metering device, or low load conditions.


Question 5 A scroll compressor differs from a reciprocating compressor in that it:

A. Uses pistons and cylinders for compression

B. Requires valve plates for compression

C. Uses two spiral-shaped scrolls to compress refrigerant

D. Operates only in cooling mode
E. Cannot be used with HFC refrigerants

,CORRECT ANSWER: C RATIONALE: Scroll compressors use two interleaved spiral
scrolls — one fixed, one orbiting — to progressively compress refrigerant. They are
more efficient, quieter, and have fewer moving parts than reciprocating compressors,
making them popular in modern residential and commercial HVAC systems.


Question 6 What does subcooling measure in a refrigeration system?

A. Temperature difference across the evaporator

B. Refrigerant temperature at suction line

C. How many degrees below saturation temperature the liquid refrigerant is
cooled

D. Pressure difference across the metering device

E. Temperature rise of air across the condenser

CORRECT ANSWER: C RATIONALE: Subcooling is measured at the condenser
outlet and indicates how many degrees the liquid refrigerant has been cooled below its
condensing (saturation) temperature. Adequate subcooling (typically 10–20°F) ensures
liquid refrigerant reaches the metering device without flashing, which would reduce
system efficiency.


Question 7 A technician finds oil logging in the evaporator. What is the most likely
cause?
A. Overcharge of refrigerant

B. Insufficient refrigerant velocity to return oil to the compressor

C. High ambient temperature

D. Oversized metering device

E. Excessive subcooling

CORRECT ANSWER: B RATIONALE: Oil logging occurs when refrigerant velocity in
the evaporator is too low to carry oil back to the compressor. This is often caused by an
oversized system, low load conditions, or improper piping design. Oil accumulation in
the evaporator reduces heat transfer efficiency and can starve the compressor of
lubrication.

, Question 8 Which tool is used to measure refrigerant manifold pressures?

A. Psychrometric chart

B. Anemometer

C. Manifold gauge set

D. Megohmmeter

E. Combustion analyzer

CORRECT ANSWER: C RATIONALE: A manifold gauge set connects to the high-side
and low-side service ports of a refrigeration system to measure suction and discharge
pressures. These pressure readings, when compared to saturation temperature charts,
help diagnose refrigerant charge, system operation, and component faults.



Question 9 What is the saturation temperature of R-410A at 300 psig?
A. 40°F

B. Approximately 105°F

C. 70°F

D. 130°F

E. 55°F

CORRECT ANSWER: B RATIONALE: Using a pressure-temperature chart for R-
410A, 300 psig corresponds to approximately 105°F saturation temperature.
Understanding P-T relationships is critical for diagnosing refrigerant charge and system
performance, as they directly indicate what condensing or evaporating conditions are
occurring.


Question 10 A system operating with high suction pressure and high discharge
pressure most likely has:

A. A refrigerant undercharge

B. A restricted liquid line

C. An overcharge of refrigerant

D. A failed compressor