First Class Stationary Air Conditioning - 636-LA Contractor Exam
100 Multiple Choice Questions with Answer Key and Explanations
**1.** Which organization's standards are primarily referenced for refrigerant piping in
stationary air conditioning systems?
A) ASHRAE
B) UL
C) ARI
D) ASME
**Answer:** A
**Explanation:** ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning
Engineers) standards, particularly ASHRAE 15 and 34, govern refrigerant safety and piping
requirements.
**2.** What is the minimum thickness for Type L copper refrigerant tubing used in a 100
psig system?
A) 0.025 inches
B) 0.032 inches
C) 0.040 inches
D) 0.050 inches
**Answer:** B
**Explanation:** Type L copper (medium thickness) is commonly used for refrigerant lines;
0.032" is typical wall thickness for smaller diameters in refrigeration service.
**3.** According to ASHRAE Standard 15, what is the maximum refrigerant charge allowed
for a direct expansion system in an occupied space without additional ventilation?
A) Based on room volume and refrigerant safety classification
B) 10 pounds regardless of room size
,C) 25 pounds for all refrigerants
D) No limit if using R-410A
**Answer:** A
**Explanation:** Maximum charge is calculated based on room volume (lbs/1000 ft³) and
refrigerant's safety group (A1, A2, B1, B2).
**4.** What is the primary purpose of a crankcase heater on a compressor?
A) To improve compression efficiency
B) To prevent refrigerant migration and oil dilution during off-cycle
C) To reduce starting current
D) To preheat suction gas
**Answer:** B
**Explanation:** Crankcase heaters prevent liquid refrigerant from accumulating in the
compressor oil during off-cycles, which could cause damage at start-up.
**5.** Which component is used to protect a compressor from liquid slugging?
A) Suction accumulator
B) Discharge muffler
C) Oil separator
D) Check valve
**Answer:** A
**Explanation:** Suction accumulators collect and vaporize liquid refrigerant before it
reaches the compressor.
**6.** What is the minimum recommended velocity for refrigerant suction lines to ensure
proper oil return?
A) 500 fpm
,B) 750 fpm
C) 1000 fpm
D) 1500 fpm
**Answer:** A
**Explanation:** Minimum velocities of 500-700 fpm in suction lines and 1000-1800 fpm in
discharge lines help carry oil through the system.
**7.** For a rooftop unit with a 50-foot refrigerant line set, what is typically required?
A) No special considerations
B) Larger diameter piping
C) Oil traps every 20 feet
D) Suction line accumulator
**Answer:** D
**Explanation:** Long suction lines may require accumulators to prevent liquid floodback
to the compressor during off-cycles.
**8.** What is the purpose of a sight glass in the liquid line?
A) To check oil level
B) To monitor refrigerant charge via bubble indication
C) To observe compressor operation
D) To check for moisture
**Answer:** B
**Explanation:** A sight glass in the liquid line shows bubbles if the system is
undercharged or has restrictions.
**9.** According to ASHRAE 34, which refrigerant classification has lower toxicity and
higher flammability?
, A) A1
B) A2
C) B1
D) B2
**Answer:** B
**Explanation:** A2 = lower toxicity, higher flammability; A1 = lower toxicity, no flame
propagation; B1 = higher toxicity, lower flammability; B2 = higher toxicity, higher
flammability.
**10.** What is the maximum allowable pressure drop in a refrigerant liquid line?
A) Equivalent to 1°F temperature change
B) Equivalent to 2°F temperature change
C) Equivalent to 3°F temperature change
D) Equivalent to 5°F temperature change
**Answer:** B
**Explanation:** Typically limited to pressure drop equivalent to 1-2°F saturation
temperature change to prevent flash gas at the expansion device.
**11.** Which brazing alloy is suitable for copper-to-copper joints in R-410A systems?
A) 50/50 tin-lead solder
B) 95/5 tin-antimony solder
C) 15% silver phosphorus-copper (BCuP)
D) 0% silver phosphorus-copper
**Answer:** C
**Explanation:** BCuP alloys (15%, 5%, or 0% silver) are commonly used for copper-to-
copper joints; higher silver content for stronger joints in high-pressure systems like R-410A.
100 Multiple Choice Questions with Answer Key and Explanations
**1.** Which organization's standards are primarily referenced for refrigerant piping in
stationary air conditioning systems?
A) ASHRAE
B) UL
C) ARI
D) ASME
**Answer:** A
**Explanation:** ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning
Engineers) standards, particularly ASHRAE 15 and 34, govern refrigerant safety and piping
requirements.
**2.** What is the minimum thickness for Type L copper refrigerant tubing used in a 100
psig system?
A) 0.025 inches
B) 0.032 inches
C) 0.040 inches
D) 0.050 inches
**Answer:** B
**Explanation:** Type L copper (medium thickness) is commonly used for refrigerant lines;
0.032" is typical wall thickness for smaller diameters in refrigeration service.
**3.** According to ASHRAE Standard 15, what is the maximum refrigerant charge allowed
for a direct expansion system in an occupied space without additional ventilation?
A) Based on room volume and refrigerant safety classification
B) 10 pounds regardless of room size
,C) 25 pounds for all refrigerants
D) No limit if using R-410A
**Answer:** A
**Explanation:** Maximum charge is calculated based on room volume (lbs/1000 ft³) and
refrigerant's safety group (A1, A2, B1, B2).
**4.** What is the primary purpose of a crankcase heater on a compressor?
A) To improve compression efficiency
B) To prevent refrigerant migration and oil dilution during off-cycle
C) To reduce starting current
D) To preheat suction gas
**Answer:** B
**Explanation:** Crankcase heaters prevent liquid refrigerant from accumulating in the
compressor oil during off-cycles, which could cause damage at start-up.
**5.** Which component is used to protect a compressor from liquid slugging?
A) Suction accumulator
B) Discharge muffler
C) Oil separator
D) Check valve
**Answer:** A
**Explanation:** Suction accumulators collect and vaporize liquid refrigerant before it
reaches the compressor.
**6.** What is the minimum recommended velocity for refrigerant suction lines to ensure
proper oil return?
A) 500 fpm
,B) 750 fpm
C) 1000 fpm
D) 1500 fpm
**Answer:** A
**Explanation:** Minimum velocities of 500-700 fpm in suction lines and 1000-1800 fpm in
discharge lines help carry oil through the system.
**7.** For a rooftop unit with a 50-foot refrigerant line set, what is typically required?
A) No special considerations
B) Larger diameter piping
C) Oil traps every 20 feet
D) Suction line accumulator
**Answer:** D
**Explanation:** Long suction lines may require accumulators to prevent liquid floodback
to the compressor during off-cycles.
**8.** What is the purpose of a sight glass in the liquid line?
A) To check oil level
B) To monitor refrigerant charge via bubble indication
C) To observe compressor operation
D) To check for moisture
**Answer:** B
**Explanation:** A sight glass in the liquid line shows bubbles if the system is
undercharged or has restrictions.
**9.** According to ASHRAE 34, which refrigerant classification has lower toxicity and
higher flammability?
, A) A1
B) A2
C) B1
D) B2
**Answer:** B
**Explanation:** A2 = lower toxicity, higher flammability; A1 = lower toxicity, no flame
propagation; B1 = higher toxicity, lower flammability; B2 = higher toxicity, higher
flammability.
**10.** What is the maximum allowable pressure drop in a refrigerant liquid line?
A) Equivalent to 1°F temperature change
B) Equivalent to 2°F temperature change
C) Equivalent to 3°F temperature change
D) Equivalent to 5°F temperature change
**Answer:** B
**Explanation:** Typically limited to pressure drop equivalent to 1-2°F saturation
temperature change to prevent flash gas at the expansion device.
**11.** Which brazing alloy is suitable for copper-to-copper joints in R-410A systems?
A) 50/50 tin-lead solder
B) 95/5 tin-antimony solder
C) 15% silver phosphorus-copper (BCuP)
D) 0% silver phosphorus-copper
**Answer:** C
**Explanation:** BCuP alloys (15%, 5%, or 0% silver) are commonly used for copper-to-
copper joints; higher silver content for stronger joints in high-pressure systems like R-410A.
