HVAC Troubleshooting – System Diagnostics:
Covering Refrigeration Cycle Diagnostics, Superheat
and Subcooling Analysis, Electrical Circuit Testing
and Fault I Complete Study Questions with Correct
Answers for a Guarantee Exam Success | Brand New
Version
1. What is step One of troubleshooting an HVAC system - ANSWER Turn
thermostat on to desired temperature and setting
Rationale: Troubleshooting starts with verifying the "call for service." You
must ensure the controls are actually asking the system to run before checking
mechanical parts.
2. If neither the indoor or outdoor unit comes on what do you check -
ANSWER The transformer for 24V and 240V
Rationale: The transformer is the bridge between the high-power source
($240\text{V}$) and the control system ($24\text{V}$). If it fails, the "brain"
of the system has no power to signal any components.
3. If the transformer isn't getting 240V what should you then check -
ANSWER check fuses in the disconnect box, check circuit breaker, then
check transformer itself
Rationale: This follows the power backwards to the source. If there is no
primary voltage, the issue is likely a tripped safety (breaker) or a blown fuse in
the electrical supply line.
,4. What do you measure on a transformer to see if it's working - ANSWER
primary and secondary windings for resistance
Rationale: Resistance (Ohms) testing checks the integrity of the internal copper
coils. An "open" reading means the wire is broken; a "short" means the
insulation has melted.
5. if contactor pulls in but compressor, fan dosen't run what do you check -
ANSWER check for 240V to outdoor unit terminals
Rationale: If the contactor pulls in, the $24\text{V}$ control side is working. If
nothing happens, the high-voltage "muscle" power isn't reaching the motor
terminals.
6. what are 4 things technicians check to ensure the refrigerant system is
running properly - ANSWER High pressure, low pressure, subcooling,
superheat
Rationale: These four data points provide a complete "map" of the system's
health, showing how the refrigerant is moving, absorbing heat, and rejecting
heat.
7. which side is subcooling measured on - ANSWER high pressure discharge
side
Rationale: Subcooling occurs after the gas has condensed into a liquid in the
condenser; therefore, it must be measured on the high-pressure liquid line.
8. which side is superheat measure on - ANSWER low pressure suction side
Rationale: Superheat is the heat added to the vapor after it boils in the
evaporator; it is measured on the suction line before it enters the compressor.
, 9. how do you measure superheat - ANSWER actual suction temperature
minus saturation temperature
Rationale: This calculation tells you how many degrees the refrigerant has
warmed up above its boiling point, ensuring no liquid is left.
10.how do you measure subcooling - ANSWER saturation temperature minus
actual liquid temperature
Rationale: This tells you how much the liquid has cooled below its condensing
point, ensuring it is a solid column of liquid before reaching the expansion
valve.
11.What is the real job of an HVAC cooling system? - ANSWER To move heat
from inside the house to outside — not to create cold.
Rationale: According to the laws of thermodynamics, "cold" is just the absence
of heat. The system acts as a heat sponge, soaking it up inside and squeezing it
out outside.
12.Cooling equals removing what from the home? - ANSWER Heat energy.
Rationale: Air conditioning is a process of energy transfer. We measure this
energy removal in BTUs.
13.Which comes first: airflow or refrigerant performance? - ANSWER Airflow
comes first.
Rationale: Refrigerant cannot move heat if there isn't enough air passing over
the coils. You cannot diagnose a gas problem until you've confirmed an air
solution.
Covering Refrigeration Cycle Diagnostics, Superheat
and Subcooling Analysis, Electrical Circuit Testing
and Fault I Complete Study Questions with Correct
Answers for a Guarantee Exam Success | Brand New
Version
1. What is step One of troubleshooting an HVAC system - ANSWER Turn
thermostat on to desired temperature and setting
Rationale: Troubleshooting starts with verifying the "call for service." You
must ensure the controls are actually asking the system to run before checking
mechanical parts.
2. If neither the indoor or outdoor unit comes on what do you check -
ANSWER The transformer for 24V and 240V
Rationale: The transformer is the bridge between the high-power source
($240\text{V}$) and the control system ($24\text{V}$). If it fails, the "brain"
of the system has no power to signal any components.
3. If the transformer isn't getting 240V what should you then check -
ANSWER check fuses in the disconnect box, check circuit breaker, then
check transformer itself
Rationale: This follows the power backwards to the source. If there is no
primary voltage, the issue is likely a tripped safety (breaker) or a blown fuse in
the electrical supply line.
,4. What do you measure on a transformer to see if it's working - ANSWER
primary and secondary windings for resistance
Rationale: Resistance (Ohms) testing checks the integrity of the internal copper
coils. An "open" reading means the wire is broken; a "short" means the
insulation has melted.
5. if contactor pulls in but compressor, fan dosen't run what do you check -
ANSWER check for 240V to outdoor unit terminals
Rationale: If the contactor pulls in, the $24\text{V}$ control side is working. If
nothing happens, the high-voltage "muscle" power isn't reaching the motor
terminals.
6. what are 4 things technicians check to ensure the refrigerant system is
running properly - ANSWER High pressure, low pressure, subcooling,
superheat
Rationale: These four data points provide a complete "map" of the system's
health, showing how the refrigerant is moving, absorbing heat, and rejecting
heat.
7. which side is subcooling measured on - ANSWER high pressure discharge
side
Rationale: Subcooling occurs after the gas has condensed into a liquid in the
condenser; therefore, it must be measured on the high-pressure liquid line.
8. which side is superheat measure on - ANSWER low pressure suction side
Rationale: Superheat is the heat added to the vapor after it boils in the
evaporator; it is measured on the suction line before it enters the compressor.
, 9. how do you measure superheat - ANSWER actual suction temperature
minus saturation temperature
Rationale: This calculation tells you how many degrees the refrigerant has
warmed up above its boiling point, ensuring no liquid is left.
10.how do you measure subcooling - ANSWER saturation temperature minus
actual liquid temperature
Rationale: This tells you how much the liquid has cooled below its condensing
point, ensuring it is a solid column of liquid before reaching the expansion
valve.
11.What is the real job of an HVAC cooling system? - ANSWER To move heat
from inside the house to outside — not to create cold.
Rationale: According to the laws of thermodynamics, "cold" is just the absence
of heat. The system acts as a heat sponge, soaking it up inside and squeezing it
out outside.
12.Cooling equals removing what from the home? - ANSWER Heat energy.
Rationale: Air conditioning is a process of energy transfer. We measure this
energy removal in BTUs.
13.Which comes first: airflow or refrigerant performance? - ANSWER Airflow
comes first.
Rationale: Refrigerant cannot move heat if there isn't enough air passing over
the coils. You cannot diagnose a gas problem until you've confirmed an air
solution.
