CFC Alternative Refrigerants & Transitions 2 — Questions and Answers
Question 1: R-410A is classified as which type of refrigerant blend?
- Azeotropic blend
- Zeotropic blend (Correct answer)
- Single-component refrigerant
- Hydrocarbon blend
Correct answer: Zeotropic blend
R-410A is a zeotropic (near-azeotropic) HFC blend of R-32 and R-125 that exhibits some temperature glide.
Question 2: Which property of HFO refrigerants contributes most to their low Global Warming Potential (GWP)?
- They contain chlorine atoms
- They degrade quickly in the atmosphere (Correct answer)
- They have high boiling points
- They are insoluble in water
Correct answer: They degrade quickly in the atmosphere
HFOs have a very short atmospheric lifetime (days) because they break down rapidly in the troposphere, resulting in very low GWP values.
Question 3: What is the primary reason R-22 systems cannot simply be retrofitted with R-410A?
- R-410A is flammable
- R-410A operates at much higher pressures (Correct answer)
- R-410A requires a different oil type only
- R-410A has a lower cooling capacity
Correct answer: R-410A operates at much higher pressures
R-410A operates at pressures approximately 70% higher than R-22, requiring equipment rated for higher pressure ratings.
Question 4: R-407C was developed primarily as a drop-in replacement for which refrigerant?
- R-12
- R-134a
- R-22 (Correct answer)
- R-502
Correct answer: R-22
R-407C is an HFC blend designed to approximate R-22 performance characteristics for retrofit applications in air conditioning systems.
Question 5: What does the term 'temperature glide' refer to in refrigerant blends?
- The rate at which refrigerant cools the compressor
- The difference in boiling temperature between the lightest and heaviest components during phase change (Correct answer)
- The temperature drop across the expansion valve
- The superheat range at the evaporator outlet
Correct answer: The difference in boiling temperature between the lightest and heaviest components during phase change
Temperature glide is the difference in saturation temperatures between the dew point and bubble point of a zeotropic blend during evaporation or condensation.
Question 6: Which refrigerant is classified as A2L (mildly flammable) and used as a replacement for R-22 in some applications?
- R-134a
- R-32 (Correct answer)
- R-404A
- R-507A
Correct answer: R-32
R-32 is classified A2L due to its mild flammability and is used as a replacement for R-22 and R-410A, with a GWP of 675.
Question 7: When transitioning a system from R-404A to a lower-GWP alternative, which step is most critical before introducing the new refrigerant?
- Replacing only the expansion valve
- Recovering all R-404A and flushing residual oil if required (Correct answer)
- Pressurizing the system with nitrogen first
- Replacing the condenser coil
Correct answer: Recovering all R-404A and flushing residual oil if required
Complete recovery of the existing refrigerant and flushing mineral or alkylbenzene oil prevents contamination and ensures proper miscibility with the new refrigerant's required oil.
CFC Alternative Refrigerants & Transitions 2
R-410A is classified as which type of refrigerant blend?