310S Heating, Ventilation and Air Conditioning (HVAC) 1 — Questions and Answers
Question 1: What refrigerant replaced R-12 (Freon) in automotive A/C systems to reduce ozone depletion?
- R-22
- R-410A
- R-134a (Correct answer)
- R-1234yf
Correct answer: R-134a
R-134a replaced R-12 due to its significantly lower ozone depletion potential, becoming mandatory in North American vehicles after 1995.
Question 2: What is the primary function of the receiver-drier in an automotive A/C system?
- To compress the refrigerant vapour
- To remove moisture and filter contaminants from the refrigerant (Correct answer)
- To rapidly expand refrigerant and lower its temperature
- To transfer heat from cabin air to the refrigerant
Correct answer: To remove moisture and filter contaminants from the refrigerant
The receiver-drier stores liquid refrigerant, removes moisture using a desiccant, and filters contaminants from the high-pressure liquid line.
Question 3: In an A/C system using a fixed orifice tube, which component stores refrigerant and separates liquid from vapour on the low side?
- Receiver-drier
- Condenser
- Accumulator (Correct answer)
- Thermostatic expansion valve
Correct answer: Accumulator
The accumulator is located on the low-pressure side between the evaporator and compressor, storing excess refrigerant and preventing liquid slugging at the compressor.
Question 4: In what physical state does refrigerant enter the evaporator during normal A/C system operation?
- High-pressure superheated vapour
- Low-pressure liquid/vapour mixture (Correct answer)
- High-pressure subcooled liquid
- Low-pressure superheated vapour
Correct answer: Low-pressure liquid/vapour mixture
After passing through the expansion device, refrigerant enters the evaporator as a low-pressure liquid/vapour mixture, absorbing heat from cabin air as it evaporates.
Question 5: What is the primary function of the condenser in an automotive A/C system?
- To absorb heat from the passenger compartment
- To filter and dry the refrigerant
- To release heat from the refrigerant to the outside air (Correct answer)
- To compress refrigerant vapour to high pressure
Correct answer: To release heat from the refrigerant to the outside air
The condenser removes heat from high-pressure refrigerant vapour, causing it to condense into a liquid as outside air flows through its fins.
Question 6: In a TXV-type A/C system, what does the sensing bulb on the thermostatic expansion valve monitor?
- Condenser outlet temperature
- Compressor discharge pressure
- Evaporator outlet temperature and pressure (Correct answer)
- Cabin air temperature
Correct answer: Evaporator outlet temperature and pressure
The TXV sensing bulb monitors evaporator outlet temperature and pressure to regulate refrigerant flow, maintaining optimal evaporator superheat.
Question 7: What is the typical low-side (suction) pressure range for a properly charged R-134a system at approximately 25°C ambient temperature?
- 0–35 kPa (0–5 psi)
- 138–207 kPa (20–30 psi) (Correct answer)
- 414–483 kPa (60–70 psi)
- 690–827 kPa (100–120 psi)
Correct answer: 138–207 kPa (20–30 psi)
A properly charged R-134a system typically shows low-side pressures of 138–207 kPa (20–30 psi) at 25°C ambient, corresponding to evaporator temperatures just above 0°C.
310S Heating, Ventilation and Air Conditioning (HVAC) 1
What refrigerant replaced R-12 (Freon) in automotive A/C systems to reduce ozone depletion?