California HVAC Contractor License
Exam (C-20) Questions And Correct
Answers (Verified Answers) Plus
Rationales 2025 Q&A | Instant
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1. What is the minimum clearance required between the top of a gas
furnace and a combustible ceiling?
A. 6 inches
B. 3 inches
C. 1 inch
D. 0 inches
Most gas furnaces require at least 1 inch of clearance from
combustibles to prevent fire hazards.
2. Which type of refrigerant is being phased out due to its ozone
depletion potential?
A. R-410A
B. R-134a
C. R-22
D. R-1234yf
R-22 is a hydrochlorofluorocarbon (HCFC) that contributes to ozone
depletion and is being phased out per EPA guidelines.
,3. What is the purpose of a TXV (Thermostatic Expansion Valve) in an
HVAC system?
A. Increase compressor efficiency
B. Control the amount of refrigerant entering the evaporator
C. Reduce fan noise
D. Regulate room humidity
The TXV modulates refrigerant flow into the evaporator based on
cooling demand.
4. When brazing refrigerant lines, what gas is typically used as a purge to
prevent oxidation?
A. Oxygen
B. Propane
C. Butane
D. Nitrogen
Nitrogen is used as a purge gas to prevent oxidation and scale
buildup inside the lines.
5. A residential HVAC system with a SEER rating of 14 means:
A. It has a 14-year warranty
B. It has a seasonal energy efficiency ratio of 14
C. It uses 14 pounds of refrigerant
D. It runs at 14 volts
SEER measures energy efficiency; a higher SEER indicates better
performance.
6. What is the minimum slope for horizontal condensate drain lines?
A. 1/2 inch per foot
B. 1/8 inch per foot
C. 1/4 inch per foot
D. Level is acceptable
, A minimum slope of 1/4 inch per foot ensures proper drainage and
prevents clogging.
7. In ductwork installation, what is the main purpose of mastic or duct
sealant?
A. Prevent rust
B. Reduce vibration
C. Seal air leaks
D. Prevent odors
Duct sealants reduce energy loss by preventing air leaks at joints and
seams.
8. Which of the following wire colors is typically used for 24V control
power in HVAC?
A. Green
B. Yellow
C. White
D. Red
Red is conventionally used for 24V power from the transformer.
9. What is the most accurate method to determine superheat in a fixed
orifice system?
A. Subcooling method
B. Temperature and pressure reading at the suction line
C. Measuring supply air temperature
D. Measuring return air humidity
Superheat is calculated using suction pressure and suction line
temperature.
10. What should be done before recovering refrigerant from a
system?
A. Check voltage
B. Identify the type of refrigerant
Exam (C-20) Questions And Correct
Answers (Verified Answers) Plus
Rationales 2025 Q&A | Instant
Download Pdf
1. What is the minimum clearance required between the top of a gas
furnace and a combustible ceiling?
A. 6 inches
B. 3 inches
C. 1 inch
D. 0 inches
Most gas furnaces require at least 1 inch of clearance from
combustibles to prevent fire hazards.
2. Which type of refrigerant is being phased out due to its ozone
depletion potential?
A. R-410A
B. R-134a
C. R-22
D. R-1234yf
R-22 is a hydrochlorofluorocarbon (HCFC) that contributes to ozone
depletion and is being phased out per EPA guidelines.
,3. What is the purpose of a TXV (Thermostatic Expansion Valve) in an
HVAC system?
A. Increase compressor efficiency
B. Control the amount of refrigerant entering the evaporator
C. Reduce fan noise
D. Regulate room humidity
The TXV modulates refrigerant flow into the evaporator based on
cooling demand.
4. When brazing refrigerant lines, what gas is typically used as a purge to
prevent oxidation?
A. Oxygen
B. Propane
C. Butane
D. Nitrogen
Nitrogen is used as a purge gas to prevent oxidation and scale
buildup inside the lines.
5. A residential HVAC system with a SEER rating of 14 means:
A. It has a 14-year warranty
B. It has a seasonal energy efficiency ratio of 14
C. It uses 14 pounds of refrigerant
D. It runs at 14 volts
SEER measures energy efficiency; a higher SEER indicates better
performance.
6. What is the minimum slope for horizontal condensate drain lines?
A. 1/2 inch per foot
B. 1/8 inch per foot
C. 1/4 inch per foot
D. Level is acceptable
, A minimum slope of 1/4 inch per foot ensures proper drainage and
prevents clogging.
7. In ductwork installation, what is the main purpose of mastic or duct
sealant?
A. Prevent rust
B. Reduce vibration
C. Seal air leaks
D. Prevent odors
Duct sealants reduce energy loss by preventing air leaks at joints and
seams.
8. Which of the following wire colors is typically used for 24V control
power in HVAC?
A. Green
B. Yellow
C. White
D. Red
Red is conventionally used for 24V power from the transformer.
9. What is the most accurate method to determine superheat in a fixed
orifice system?
A. Subcooling method
B. Temperature and pressure reading at the suction line
C. Measuring supply air temperature
D. Measuring return air humidity
Superheat is calculated using suction pressure and suction line
temperature.
10. What should be done before recovering refrigerant from a
system?
A. Check voltage
B. Identify the type of refrigerant
