HVAC Refrigeration 3 — Questions and Answers
Question 1: What does a high-pressure cutout switch do in a refrigeration system?
- Stops the system when suction pressure drops too low
- Stops the compressor when discharge pressure exceeds a safe limit (Correct answer)
- Activates the condenser fan when head pressure rises
- Modulates refrigerant flow at high loads
Correct answer: Stops the compressor when discharge pressure exceeds a safe limit
A high-pressure cutout switch shuts off the compressor when discharge pressure exceeds a preset limit to prevent equipment damage.
Question 2: What is the primary purpose of an accumulator in a refrigeration system?
- Store extra refrigerant charge for high-demand periods
- Prevent liquid refrigerant from entering the compressor (Correct answer)
- Increase the suction pressure to the compressor
- Remove non-condensable gases from the system
Correct answer: Prevent liquid refrigerant from entering the compressor
An accumulator is installed in the suction line to catch any liquid refrigerant before it reaches the compressor, preventing compressor damage from liquid slugging.
Question 3: What is the Global Warming Potential (GWP) used to measure?
- The ozone depletion potential of a refrigerant over 100 years
- The heat-trapping ability of a refrigerant relative to CO2 over 100 years (Correct answer)
- The flammability rating of a refrigerant
- The efficiency of a refrigerant in a given system
Correct answer: The heat-trapping ability of a refrigerant relative to CO2 over 100 years
GWP measures how much heat a greenhouse gas traps compared to CO2 over a 100-year period, with CO2 having a GWP of 1.
Question 4: In a refrigeration system, 'head pressure' refers to which pressure?
- Suction line pressure at the compressor inlet
- Discharge pressure at the compressor outlet (Correct answer)
- Evaporator pressure measured at the inlet
- Pressure drop across the expansion valve
Correct answer: Discharge pressure at the compressor outlet
Head pressure is the high-side discharge pressure measured at the compressor outlet, representing the condensing pressure of the refrigerant.
Question 5: What refrigerant safety classification is assigned to ammonia (R-717)?
- A1 (non-toxic, non-flammable)
- A2L (low flammability)
- B2L (toxic, low flammability) (Correct answer)
- B3 (toxic, high flammability)
Correct answer: B2L (toxic, low flammability)
Ammonia is classified B2L — toxic (B) and mildly flammable (2L) — making it effective for industrial refrigeration but requiring special safety precautions.
Question 6: What is the effect of non-condensable gases (such as air or nitrogen) in a refrigeration system?
- They lower the suction pressure and increase efficiency
- They raise the condensing pressure and reduce system efficiency (Correct answer)
- They help lubricate the compressor valves
- They prevent moisture from freezing in the expansion valve
Correct answer: They raise the condensing pressure and reduce system efficiency
Non-condensable gases accumulate in the condenser, raising condensing pressure and head pressure, which reduces efficiency and can cause high-pressure cutouts.
Question 7: What does the term 'ton of refrigeration' represent?
- The weight of refrigerant in a fully charged system
- 12,000 BTU/hr of heat removal capacity (Correct answer)
- The compressor capacity measured in horsepower
- 1,000 BTU/hr of cooling capacity
Correct answer: 12,000 BTU/hr of heat removal capacity
One ton of refrigeration equals 12,000 BTU/hr, originally based on the heat required to melt one ton of ice in 24 hours.
HVAC Refrigeration 3
What does a high-pressure cutout switch do in a refrigeration system?